remove tail_log
remove tail_log

tail_log is deprecated and should be removed
https://github.com/openstack/devstack/blob/master/functions-common#L1611

Change-Id: I6012fd63aa6b0cdb8ed1b278880f8f6c3e4d38cf

openstack/watcher,stackforge/watcher,stackforge/watcher,openstack/watcher