Fix occasional regression test 003.failover failure.

Fix occasional regression test 003.failover failure.

The test compares the result of show pool_nodes against pre-computed
expected text file. After primary node goes down and old standby
promotes to primary, it is possible that streaming replication worker
process stores the replication state (async, streaming) in shared
memory before the failover but fails to update the state after the
failover. Fix is, replace "async", "streaming" with space characters
in the result file to match the expected file.