`snap services` should indicate when services are a oneshot

[Dan Watkins]

When I run `snap services` with a couple of Canonical snaps installed, I see the following:

Service Startup Current
canonical-livepatch.canonical-livepatchd enabled inactive
lxd.activate enabled inactive
lxd.daemon enabled active

This suggests to me that canonical-livepatch.canonical-livepatchd and lxd.activate are in some way broken (as if they're enabled it's reasonable to think that they should be active). In canonical-livepatch's case, my intuition is correct; I'm on 18.10 so the service fails to start. lxd.activate, on the other hand, is a oneshot service, so it's not in an error state at all; it's done everything it needs to do.

It would be good if `snap services` distinguished between these two cases.

[Zygmunt Krynicki (zyga)]

This feels like a papercut but it also needs UX design. I'll relay this issue to my colleague who is looking into snap service management now.

[Ian Johnson (anonymouse67)]

We will be working on some UX changes to `snap services`, namely the changes mentioned at https://forum.snapcraft.io/t/how-to-manage-services-with-sockets-timers/7904/8?u=ijohnson

We don't currently have plans to expose the type of service in the snap services output, but we are exploring having a `snap services --verbose` which seems like a natural place to put this.