Running ghost setup should be (more) idempotent

[acburdine]

A user reported a case where they ended up with two systemd service files, one called ghost_<ip address of blog> and one called ghost_<url of blog>. Not for sure on how this happened, but based on the current code I have a theory:

• User runs ghost setup, gives ip address as url
• After a while, user runs ghost setup again, but gives the actual domain name this time

In this case, ghost setup could potentially set up two different systemd service files, because the ghost instance "name" is generated by using the url (see here). Quick fix would probably be to skip the setup step that sets the instance name if the name is already set....however it's probably worth investigating further to see if there are more things in the setup command that can be fixed to make it idempotent.

If I find more things, I will add them here:

• Ensure instance name doesn't get reset if it already exists