Release jobs use Gerrit Trigger choosing strategy

Use choosing strategy Gerrit Trigger in container/jar and
package cloud release merge jobs. This retains the current
behavior in the simple merge case, and ensures that a job
triggered by a "remerge" comment uses the release file at
that commit.  The previous choosing strategy, default, uses
the tip of the target branch.  That does not allow recovery
from merge job failure if the target branch has advanced past
the commit with the release file.

Change-Id: I6685e54da9f1510243f52506794cf52a28b9eb61
Signed-off-by: Lott, Christopher (cl778h) <cl778h@att.com>