HA: Add support for configuring a new appliance with the existing primary node number used in the prior pg_basebackup/pg_dumpall

[jrafanie]

pg_basebackup and pg_dumpall will bring over the HA node information on a restore. With this the case, the new replacement appliance that has this database restored will have the HA node configuration set in the database but the repmgr service will not be configured, started, etc. Our existing code assumes you're configuring repmgr and the new node name together. You can't do just one of them.

Primaries will blow up with this node is already registered.

On the other hand, if you've configured a standby with an existing node number, you're prompted if you really want to reuse the same number