Fix update cloud image list job to handle newlines

Fix update cloud image list job to handle newlines

Fix update cloud image list job to handle newlines correctly and
update an existing gerrit change request.

A gerrit change submitted through git-review checks for an
existing change-id on Gerrit and either updates the patchset or
creates a new one. For this to work correctly the change-id
should go into the commit footer and not in the
GERRIT_COMMIT_MESSAGE. The embedded newlines are not processed
correctly in the script and fails to separate the footer and the
GERRIT_COMMIT_MESSAGE, instead it creates a new patches everytime
rather than updating an existing one.

The change is tested and now existing CR's are updated rather than
pushing a new CR everytime.

https://git.opendaylight.org/gerrit/c/releng/builder/+/89136

Issue: RELENG-2687
Change-Id: I8397d2d8a9402db07c99173c9f999152bc3c61ee
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>