pg_upgrade: start/stop new server after pg_resetwal

pg_upgrade:  start/stop new server after pg_resetwal

When commit 0f33a719fdbb5d8c43839ea0d2c90cd03e2af2d2 removed the
instructions to start/stop the new cluster before running rsync, it was
now possible for pg_resetwal/pg_resetxlog to leave the final WAL record
at wal_level=minimum, preventing upgraded standby servers from
reconnecting.

This patch fixes that by having pg_upgrade unconditionally start/stop
the new cluster after pg_resetwal/pg_resetxlog has run.

Backpatch through 9.2 since, though the instructions were added in PG
9.5, they worked all the way back to 9.2.

Discussion: https://postgr.es/m/20170620171844[email protected]

Backpatch-through: 9.2