Fixes Bug 1040292 - replace create with get, keeping create as fallback

whenever the Ceph crashstore wanted a bucket that it did not already have cached,it would call "create_bucket"  For a save operation, it ought to try to "get_bucket" first and on failure, then try create.
no, ```_fetch_from_boto_s3``` calls ```self._get_bucket```   while ```_submit_to_boto_s3``` calls ```self._get_or_create_bucket```