host/cli: Read singleton flag from postgres when restoring backup
host/cli: Read singleton flag from postgres when restoring backup

This ensures that we end up booting the correct number of Postgres
instances when restoring a backup from a multi-node cluster to a
single-node cluster.

Signed-off-by: Jonathan Rudenberg <3692bfa45759a67d83aedf0045f6cb635a966abf@titanous.com>
philiplb/flynn,lmars/flynn,lmars/flynn,philiplb/flynn,benbjohnson/flynn,philiplb/flynn,benbjohnson/flynn,benbjohnson/flynn,flynn/flynn,flynn/flynn,flynn/flynn,philiplb/flynn,benbjohnson/flynn,lmars/flynn,benbjohnson/flynn,flynn/flynn,lmars/flynn,benbjohnson/flynn,flynn/flynn,philiplb/flynn,lmars/flynn