In dispatch test cases, we need a way to put a segment to in-recovery
status to test gang recreating logic of dispatcher.

We used to trigger a panic fault on a segment and suspend the quickdie()
to simulate in-recovery status. To avoid segment staying in recovery mode
for a long time, we used a "sleep" fault instead of 'suspend' in quickdie(),
so segment can accept new connections after 5 seconds. 5 seconds works
fine most of time, but still not stable enough, so we decide to use more
straight-forward mean to simulate in-recovery mode which reports a
POSTMASTER_IN_RECOVERY_MSG directly in ProcessStartupPacket(). To not
affecting other backends, we create a new database so fault injectors
only affect dispatch test cases.