Don't try to compress patterns ignored by gzip.

* modules/openstack_project/files/log_archive_maintenance.sh:
According to the gzip manpage, there are a variety of filename
endings it will consider to indicate a file is already compressed
and will then refuse to compress. Some tempfiles get
randomly-generated names which match these endings, causing the
compression cron job to emit errors. Instead we make the script skip
over them.

Change-Id: Ib78a19362eaa54c43f44a9e6bd0c265dddee92be
Reviewed-on: https://review.openstack.org/34419
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins