Allow building OVS from souce

The lastest version of OVS in Ubuntu 12.04 is
quite old (1.4). 1.9 is the new LTS supported
version and 1.11 is the newest head version.

Version 1.10/1.11 has many new features and
performance improvements, so there is a benefit
in being able to install it over the default 1.4
packages.

By default, nothing changes in this patch.
You must explicitly set
['openstack']['network']['openvswitch']['use_source_version']
to true in order to enable it.

Change-Id: I3779b6b73f3e2c0a56d3bed6bf3e3a4184649c24
Merge "Allow building OVS from souce"