debugging first run of install hook is not straight forward

[Michael Nelson]

Steps to reproduce:
 1) Deploy a service
 2) Run `juju debug-hooks service-name/0`

Expected result:
 * Eventually be dropped into the install hook on the unit

Actual result:
 * ERROR unit "service-name/0" has no public address

Perhaps a --wait option to debug-hooks so current behaviour isn't modified, although I think it'd be nice as a default, with --no-wait being an option.

Currently to work around this, I typically bootstrap, add a number of machines and wait for their IP addresses to be available, deploy the service and run debug-hooks straight away. But it's still a race.