Make Travis builds on OS X work again

It's simpler and faster now, because it's no longer necessary to install
boost-python (which had changed in homebrew - the root cause of the
failures). Also removed boost-python from the Linux install.

.travis.yml

@@ -58,7 +58,6 @@ addons:
             - g++
             - clang-3.5
             - libboost-system1.55-dev
-            - libboost-python1.55-dev
             - libboost-test1.55-dev
             - libboost-program-options1.55-dev
             - libpcap-dev
@@ -69,8 +68,8 @@ addons:
             - librdmacm-dev
             - libibverbs-dev
 before_install:
-    - if [[ "$TRAVIS_OS_NAME" == "osx" && "$TEST" == "python2" ]]; then brew update; brew install python; brew reinstall boost --with-python; brew install boost-python; pip install virtualenv; virtualenv venv; source venv/bin/activate; fi
-    - if [[ "$TRAVIS_OS_NAME" == "osx" && "$TEST" == "python3" ]]; then brew update; brew install python3; brew reinstall boost --with-python3; brew install boost-python --with-python3; pyvenv venv; source venv/bin/activate; fi
+    - if [[ "$TRAVIS_OS_NAME" == "osx" && "$TEST" == "python2" ]]; then virtualenv venv; source venv/bin/activate; fi
+    - if [[ "$TRAVIS_OS_NAME" == "osx" && "$TEST" == "python3" ]]; then brew update; brew upgrade python; pyvenv venv; source venv/bin/activate; fi
 install:
 - |
     set -e