read only bookie runs replicator and does not release the under replicated lock after failing

ReplicationWorker throws BkWriteOnReadOnlyBookieException here: https://github.com/apache/bookkeeper/blob/master/bookkeeper-server/src/main/java/org/apache/bookkeeper/replication/ReplicationWorker.java#L255
and does not release the under replicated lock.

Solution:
Release the under replicated lock before throwing BkWriteOnReadOnlyBookieException and make the replication worker wait till the bookie becomes writable again.