snapcraft can't tell when multipass is installed but disabled

[Alan Pope 🍺🐧🐱 🦄]

I sometimes `snap disable multipass` because I want to quickly shut it all down so I can use virtualbox instead. (the two conflict). If I forget to `snap enable multipass` and run snapcraft, it thinks multipass isn't installed and asks to install it. Maybe the wording needs tweaking, or it could detect a disabled multipass?

$ snapcraft
You need multipass installed to build snaps which use the base keyword.
Would you like to install it now? [y/N]: y
Waiting for multipass...
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$ snap info multipass
name: multipass
summary: Ubuntu at your fingertips
publisher: Canonical✓
license: unset
description: |
  Multipass gives you Ubuntu VMs in seconds. Just run `multipass launch` and it'll do all the setup
  for you. Check out `multipass find` for a list of available images. More details you can find
  under `multipass help`.
commands:
  - multipass
  - multipass.virsh
services:
  multipass.libvirt-bin: simple, disabled, inactive
  multipass.multipassd: simple, disabled, inactive
snap-id: mA11087v6dR3IEcQLgICQVjuvhUUBUKM
tracking: beta
channels:
  stable: –
  candidate: –
  beta: 2018.12.1 (572) 111MB classic
  edge: 2018.12.1-22-g09335ce (578) 111MB classic
installed: 2018.12.1 (572) 111MB disabled,classic