connection/ssh_lxc.py: new invocation method

Now this connection can (also) be used directly indicating the LXC
container as the target (or delegated host), if the variables
`ansible_lxc_host` and `ansible_lxc_name` are provided, either in
invetory, role or task.

`ansible_lxc_host` is the inventory hostname of the LXC running physical
host.

`ansible_lxc_name` is the container name.

File `hosts.example` is provided to show how this variables can be set
up in an inventory.

connection_plugins/ssh_lxc.py

@@ -13,6 +13,10 @@
     connection: ssh_lxc
     short_description: connect via ssh client binary and then to a container with lxc-attach
     description:
+        - Normally this connection target host is the one running LXC. Roles which set variable
+          `ansible_connection` and `ansible_ssh_lxc_name` will be executed on the container.
+        - If the target host variable `ansible_lxc_host` is defined the behavior is reverted, and the connection
+          is established
         - This connection plugin allows ansible to communicate to the target machines via normal ssh command line.
         - Ansible does not expose a channel to allow communication between the user and the ssh process to accept
           a password manually to decrypt an ssh key when using this connection plugin (which is the default). The
@@ -21,14 +25,25 @@
     version_added: "2.9.6"
     options:
       host:
-          description: Hostname/ip to connect to.
+          description: Hostname/ip running LXC to connect to, or name of the container if `lxc_host` is set.
           default: inventory_hostname
           vars:
                - name: ansible_host
                - name: ansible_ssh_host
+      lxc_host:
+          descriotion: Hostname/ip running LXC, if `ansible_host` is the container.
+          vars:
+              - name: ansible_lxc_host
+          type: str
+      hostvars:
+          description: obtain invetory values for use in `delegate_to` mode with `lxc_host` set.
+          vars:
+              - name: hostvars
+          type: dict
       container_name:
-          description: name of lxc container to attach to
+          description: name of lxc container to attach to.
           vars:
+              - name: ansible_lxc_name
               - name: ansible_ssh_lxc_name
               - name: ansible_docker_extra_args
           type: str
@@ -478,7 +493,28 @@ def __init__(self, *args, **kwargs):
     # management here.
 
     def _connect(self):
-        self.container_name = self.get_option('container_name')
+        if self.get_option('lxc_host') is None:
+            self.container_name = self.get_option('container_name')
+
+            display.vvv("lxc_host=None; so container_name={}, host={}".format(self.container_name,
+                                                                              self.host))
+        else:
+            self.container_name = self.get_option('container_name')
+
+            lxc_host_hostname = self.get_option('lxc_host')
+            try:
+                lxc_host_vars = self.get_option('hostvars')[lxc_host_hostname]
+            except KeyError:
+                raise AnsibleError("ansible_lxc_host={} not found in invetory.".format(lxc_host_hostname))
+
+            self.host = lxc_host_vars['ansible_host']
+            if 'ansible_port' in lxc_host_vars:
+                self.port = lxc_host_vars['ansible_port']
+            if 'ansible_user' in lxc_host_vars:
+                self.user = lxc_host_vars['ansible_user']
+
+            display.vvv("lxc_host={1}; so container_name={0}, host={1}".format(self.container_name,
+                                                                               self.host))
         return self
 
     @staticmethod

hosts.example

@@ -0,0 +1,32 @@
+localhost             ansible_connection=local
+gandalf               ansible_host=10.150.40.1         ansible_user=root
+
+# CERTIFICATION AUTHORITIES
+authorities           ansible_host=10.150.40.8         ansible_user=root
+authorities_request   ansible_host=10.150.40.8         ansible_user=request
+
+# PHYSICAL HOST  -------------------------------------------------------------- <LVM VG Name>
+black                 ansible_host=10.150.40.42        ansible_user=root        vg_name=black-vg
+ca                    ansible_host=10.150.40.8         ansible_user=root
+
+# LXC GUEST  ------------------------------------------------------------------ <LXC Running Host> ------ <LXC Container Name>
+#blogs                ansible_host=10.150.42.17        ansible_user=root        ansible_lxc_host=black    ansible_lxc_name=blogs
+ldap                  ansible_host=10.150.42.10        ansible_user=root        ansible_lxc_host=black    ansible_lxc_name=ldap
+#lists                ansible_host=10.150.42.15        ansible_user=root
+#login                ansible_host=10.150.42.100       ansible_user=root
+#mail                 ansible_host=10.150.42.36        ansible_user=root
+#matrix               ansible_host=10.150.42.26        ansible_user=root
+#media                ansible_host=10.150.42.104       ansible_user=root
+#projects             ansible_host=10.150.42.12        ansible_user=root
+#status               ansible_host=10.150.42.103       ansible_user=root
+#users                ansible_host=10.150.42.18        ansible_user=root
+#webmail              ansible_host=10.150.42.14        ansible_user=root
+#wiki                 ansible_host=10.150.42.16        ansible_user=root
+
+# NETWORK NODES
+management_gateway    ansible_host=10.150.40.1         ansible_user=root
+vm_gateway            ansible_host=10.150.42.1         ansible_user=root
+reverse_proxy         ansible_host=10.150.42.1         ansible_user=root
+
+[vm_hosts]
+black