ENV['RELEASES'] overrides the [cuttlefish dumpling emperor]

The RELEASES environment variable contains the list of ceph releases for
which integration tests are going to be run. This is convenient to speed
up tests when debugging the logic of the implementation and before
making sure it works accross all distributions.

Change-Id: I0d0a6af6f07aeba72c42e6f853353ccf97db8658
Signed-off-by: Loic Dachary <loic@dachary.org>
Merge "ENV['RELEASES'] overrides the [cuttlefish dumpling emperor]"