Update buildrpm to include latest project changes.

This commit adds post-hydrogen changes for bgpcep and
lispflowmapping projects.

Also add changes to buildrpm.sh to build from a specific
branch.

Change-Id: Icba5360be510a94bb59a480bbcafe0e9dbf54f27
Signed-off-by: Sam Hague <shague@redhat.com>
(cherry picked from commit 42255e4cb7b8b406df0ad94a08babd7e1b7c08cc)