OVN : include source compliation functions

This patch moves the OVS compilation module from Neutron into DevStack.
It also renamed it to "ovs_source" to highlight its function, and the
include has been moved to where the rest of the includes are located.

Although this module is not required since by default DevStack installs
OVS/OVN from the host OS packages instead of compiling from source,
this is a nice to have as it avoids having bits and pieces of the code
scattered around multiple repositories.

Co-Authored-By: Lucas Alvares Gomes <lucasagomes@gmail.com>
Change-Id: I39ec9ce0a91bea05cf8c446a9767ab879ac8e8f3
2 files changed