On precise, give the option to build OVS from source

In Ubuntu 12.04 precise, the latest version of OVS available
is 1.4.0. 1.9.x is currently LTS and 1.10.2 is the newest "stable"
version.

1.10 contains significant performance enhancements and flow management
allowing OVS to scale and handle much larger workloads.

This allows you to choose to build and install a newer version of OVS
from debs (built from git sources) on precise to take advantage of
these performance and stability enhancements.

Change-Id: Ib5edd6f13867ba1f4fe09e0428436cac6b4edad8
Merge branch 'build_ovs_source' of github.com:kevinbringard/cookbook-openstack-network into build_ovs_source

Conflicts:
	attributes/default.rb

Change-Id: Ica392ece94e115dcf39796f837341f3462ba3fcd