Avoid using internal test methods in SSL tests

Avoid using internal test methods in SSL tests

The SSL tests for pg_ctl restart with an incorrect key passphrase used
the internal _update_pid method to set the pidfile after running pg_ctl
manually instead of using the supplied ->restart method. This refactors
the ->restart method to accept a fail_ok parameter like how ->start and
->stop does, and changes the SSL tests to use this instead. This removes
the need to call internal test module functions.

Reviewed-by: Melih Mutlu <m.melihmutlu@gmail.com>
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://postgr.es/m/F81643C4-D7B8-4C6B-AF18-B73839966279@yesql.se