Standardize vulcanizer API surface

Features:

• Client methods all return a specific struct type and an error.

type Client
    func NewClient(host string, port int) *Client
    func (c *Client) DrainServer(serverToDrain string) (ExcludeSettings, error)
    func (c *Client) FillAll() (ExcludeSettings, error)
    func (c *Client) FillOneServer(serverToFill string) (ExcludeSettings, error)
    func (c *Client) GetClusterExcludeSettings() (ExcludeSettings, error)
    func (c *Client) GetHealth() ([]ClusterHealth, error)
    func (c *Client) GetIndices() ([]Index, error)
    func (c *Client) GetNodes() ([]Node, error)
    func (c *Client) GetSettings() (ClusterSettings, error)
    func (c *Client) GetSnapshotStatus(repository string, snapshot string) (Snapshot, error)
    func (c *Client) GetSnapshots(repository string) ([]Snapshot, error)
    func (c *Client) SetAllocation(allocation string) (string, error)
    func (c *Client) SetSetting(setting string, value string) (string, string, error)
type ClusterHealth
type ClusterSetting
type ClusterSettings
type ExcludeSettings
type Index
type Node
type Snapshot