guess: return RH osdist for eng- dist-git branches
guess: return RH osdist for eng- dist-git branches

Red Hat's rel-eng team uses "eng-rhel-6" and "eng-rhel-7" branches in
dist-git. Return a product that begins with "RH" so that the "rdopkg
new-version" command will automatically upload new source tarballs to
the lookaside cache when operating here.

Change-Id: I65ae0183acd4633aba4e44aa4038ee81b6154197

redhat-openstack/rdopkg,redhat-openstack/rdopkg,openstack-packages/rdopkg,openstack-packages/rdopkg