When no playbooks are found, differentiate between "the api server works but is empty" vs "could not connect to remote api server"

[dmsimard]

Right now, if there's either no API server running or if there are no playbooks found, the error returned will be the same:

We should be able to tell if the remote API server is up and running by retrieving the version of ARA API server at "/", for example:

[guillaumevincent]

yes let me improve this

[dmsimard]

Tested https://review.opendev.org/#/c/661940/ and works for me !

When the server is offline or can't be reached:

When the server is online but empty:

Great work, thanks @guillaumevincent !