Add graphviz package to general list for building docs

A few projects are now gating on docs not having warnings/errors in them
during the docs build with sphinx, so developers are going to want to be
able to run 'tox -e docs' locally and fix issues.

The graphviz package is used by sphinx when building docs but you have
to get it from the distro, so this change adds the package to the
various distro lists.

Closes-Bug: #1359749

Change-Id: I7b7dee5e5d0dce6d5020b3e711f500118be163f8
Detect when Debian is used to launch libvirtd

this patch checks if os_VENDOR is ubuntu to launch
libvirt-bin service. Previously, is_ubuntu() was used, but
this function only detects if a deb packaging is used, so
there were no distinction between Ubuntu and Debian.

Change-Id: I222b71962f49896063910ff2a25e4f57be4bf819
Closes-Bug: 1361260
Ubuntu: Start openvswitch-switch service after install

Change-Id: I73a7cec67d0f0782de1598c4ebb1815726e38199
Closes-Bug: #1362782
Merge "Detect when Debian is used to launch libvirtd"
Merge "Add graphviz package to general list for building docs"
Merge "Ubuntu: Start openvswitch-switch service after install"
Merge branch 'master' of https://github.com/openstack-dev/devstack