InnoDB shutdown assumes that once the server has entered
SRV_SHUTDOWN_FLUSH_PHASE, no change to persistent data is allowed.
It was possible for the master thread to wake up while shutdown
is executing in SRV_SHUTDOWN_FLUSH_PHASE or
even in SRV_SHUTDOWN_LAST_PHASE.

We do not yet know if further crashes at shutdown are possible.
Also, we do not know if all the observed crashes could be explained
by the race conditions that we are now fixing.

srv_shutdown_print_master_pending(): Remove a redundant ut_time() call.

srv_shutdown(): Renamed from srv_master_do_shutdown_tasks().

srv_master_thread(): Do not resume after shutdown has been initiated.