Fix issues in pg_rewind with --no-ensure-shutdown/--write-recovery-conf

Fix issues in pg_rewind with --no-ensure-shutdown/--write-recovery-conf

This fixes two issues with recent features added in pg_rewind:
- --dry-run should do nothing on the target directory, but 927474c
forgot to consider that for --write-recovery-conf.
- --no-ensure-shutdown was not actually working.  There is no test
coverage for this option yet, but a subsequent patch will add that.

Author: Alexey Kondratov
Discussion: https://postgr.es/m/7ca88204-3e0b-2f4c-c8af-acadc4b266e5@postgrespro.ru