RollbackTest fixture might erroneously return from awaitReplication call in transitionToRollbackOperations

Currently, the rollback_test.js test fixture will await replication when calling transitionToRollbackOperations. If a node is in the middle of ROLLBACK, though, when this gets called, the awaitReplication call will ignore the node that is currently rolling back and return having checked 0 secondaries. It needs to properly wait for the ROLLBACK to occur, and for the node to fully transition to SECONDARY.