Fix groups-dev portal update sync issue

Groups-dev portal failed to download the release updates from
tarball.openstack.org/groups site, meanwhile the drush dsd-status tool
reported an update available status. This patch resolves this issue
and site-deploy and site-update executed when the .md5 file downloaded
from tarball site updated. The wget --timestamping options is used
to download the .md5 file in case of remote update only.

Change-Id: Iab237567e45864835274c01c8e93363c7ea8b620
Closes-Bug: #1334707
Merge "Fix groups-dev portal update sync issue"