Add param to config RPM repo to install ODL from

Add param to config RPM repo to install ODL from

Param allows user to change which version of ODL installed without
changes to puppet-opendaylight. Even better than limiting to a specific
version, the new rpm_repo param allows the user to select a the latest
RPM from a major release or SR, or a fixed and official release.

This patch includes the feature changes, rspec-puppet test changes,
Beaker test changes, in-code docs and README docs.

Change-Id: Ie01dafd485318d98410a2847e53ebd819a5cf7c3
Signed-off-by: Daniel Farrell <dfarrell@redhat.com>