task/internal/syslog: blacklist log from ceph-create-keys
task/internal/syslog: blacklist log from ceph-create-keys

the log format of ceph-create-keys is "$level:$name:$message"

Fixes: http://tracker.ceph.com/issues/20171
Signed-off-by: Kefu Chai <a4b264ee037c625052534d60505bfd0db4776ac4@redhat.com>

ktdreyer/teuthology,ktdreyer/teuthology,dmick/teuthology,SUSE/teuthology,ceph/teuthology,SUSE/teuthology,ceph/teuthology,dmick/teuthology,SUSE/teuthology,dmick/teuthology