Gerrit keyword to build distro and package as RPM/Deb

Should add a Gerrit keyword to build distribution that includes under-dev change and package the resulting tarball as a RPM/Deb using build-rpm and build-deb jobs. Can use keywords like `build-rpm` and `build-deb`. This would be very useful for downstream devs (OPNFV) who are interested in an ODL change (maybe fix for bug OPNFV's hitting) and want to consume/verify the proposed changed as a package.

Imported from: https://trello.com/c/dLhaXjE2/448-gerrit-keyword-to-build-distro-and-package-as-rpm-deb