[FIX] Removed mercurial fromthis build because is already installed i…
…n the ubuntu base image.
Mercurial is being installed here: https://github.com/Vauxoo/docker-ubuntu-base/blob/master/scripts/build-image.sh#L20
Also after upgrading pip to 10.0 is showing this error durig the build process:
Cannot uninstall 'mercurial'. It is a distutils installed project and thus we cannot accurately determine which files belong to it which would lead to only a partial uninstall.