Fix pgpool_setup so that it fail back to full restore if failed in restarting.

Fix pgpool_setup so that it fail back to full restore if failed in restarting.

While taking care of "[pgpool-general: 7456] Expected behaviour after pcp_detach_node ?"

https://www.pgpool.net/pipermail/pgpool-general/2021-March/007514.html

I noticed that restarting target server in follow primary script could
fail.  This could happen when former primary goes to down status using
pcp_detach_node.  The former primary will not start due to timeline
and LSN divergence.  To fix this, fail back to full restore using
pg_recovery if restarting server.