Fix Travis CI Python installations

Python 2.7 has been added by default in the Travis CI images, so no
need to reinstall it. Need to add pip, but ensure the python installation
picks the right site-packages.

Python3 brew default is 3.6, which is not compatible with PyInstaller,
so install 3.5 instead.

.travis.yml

@@ -1,38 +1,55 @@
+# Oldest OS X image in TravisCi at the moment is 10.10 Yosemite 
 os: osx
-osx_image: beta-xcode6.1
+osx_image: xcode6.4
 language: node_js
 node_js: '6'
 
 before_install:
   # OS extra info
   - sw_vers
   - uname -a
-  - python --version
-  - python -c "import struct; print(struct.calcsize('P') * 8)"
 
-  # Install Python 2 and 3 with pip and check versions
+  # Install Python 2 pip, ensure pip installed packages are found first
+  # Python 2 installation and path priority in Travis OS X is a bit of a mess
+  # https://github.com/travis-ci/travis-ci/issues/4194 
+  - curl -O https://bootstrap.pypa.io/get-pip.py
+  - sudo python get-pip.py
+  - rm get-pip.py
+  - sudo pip install --upgrade pip setuptools wheel
+  # Original problem is old version of "six" package lingering around
+  # https://github.com/testing-cabal/mock/issues/337
+  - export PYTHONPATH=/Library/Python/2.7/site-packages:$PYTHONPATH
+  - python -c "import sys; print(sys.path)"
+  - python -c "from six import wraps"
+
+  # Install Python 3.5 with pip, and check versions
   - brew update
-  - brew install python
-  - brew unlink python && brew link python
-  - brew install python3
-  - brew unlink python3 && brew link python3
+  - brew tap zoidbergwill/python
+  - brew install python35
+  - cp -R /usr/local/bin/pip3.5 /usr/local/bin/pip3
+  - sudo pip3 install --upgrade pip
+
   - brew install libcouchbase
   - PATH=/usr/local/bin:$PATH
   - echo $PATH
+
+  # Install Python packages (built with Python 3, tests for 2 and 3)
+  - sudo python -m pip install mock
+  - pip3 install mkdocs
+  - pip3 install pyinstaller
+
+  # Check Python, pip and package versions
+  - python -c "import sys; print(sys.executable)"
   - python --version
   - python -c "import struct; print(struct.calcsize('P') * 8)"
-  - pip --version
+  - python -m pip --version
+  - python -m pip freeze
+  - python3 -c "import sys; print(sys.executable)"
   - python3 --version
   - python3 -c "import struct; print(struct.calcsize('P') * 8)"
   - pip3 --version
-
-  # Install Python packages (built with Python 3, tests for 2 and 3)
-  - pip install mock
-  - pip3 install mkdocs
-  - pip3 install pyinstaller
-  - pyinstaller --version
-  - pip freeze
   - pip3 freeze
+  - pyinstaller --version
 
   # Travis make takes > 10 minutes, so need to increase wait
   - brew unlink node