Fix stability issue with new TAP test of pg_createsubscriber

Fix stability issue with new TAP test of pg_createsubscriber

The test introduced in 639352d904c8 has added a direct pg_ctl command to
start a node, a method that is incompatible with the teardown() routine
used at the end of the test as the PID saved in the Cluster object would
prevent the node to be shut down.  This can ultimately prevent the test
to perform its cleanup, failing on timeout.

Like pg_ctl's 001_start_stop or ssl_passphrase_callback's 001_testfunc,
this commit changes the test so a direct pg_ctl command is used to stop
the rogue node.  That should be hopefully enough to cool down the
buildfarm.

Per report from buildfarm member fairywren, which is the only animal
that is showing this issue.

Author: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Discussion: https://postgr.es/m/TY7PR01MB1455452AE9053DD2B77B74FEAF58CA@TY7PR01MB14554.jpnprd01.prod.outlook.com