workshop does not work on non-Ubuntu systems

Hi,

I cannot use workshop on an openSUSE Tumbleweed host which is supported by snapd.

```
maj 13 11:05:04 carrack systemd[1]: snap.workshop.workshopd.service: Scheduled restart job, restart counter is at 4.
maj 13 11:05:04 carrack systemd[1]: Starting Service for snap application workshop.workshopd...
maj 13 11:05:04 carrack workshop.workshopd[87635]: Acquiring state lock file
maj 13 11:05:04 carrack workshop.workshopd[87635]: Acquired state lock file
maj 13 11:05:04 carrack workshop.workshopd[87635]: cannot run workshop: Error loading "zfs" module: Failed to run: modprobe -b zfs: exit status 1 (modprobe: FATAL: Module zfs not found in directory /usr/lib/modules/7.0.3-1-default)
maj 13 11:05:04 carrack systemd[1]: snap.workshop.workshopd.service: Main process exited, code=exited, status=1/FAILURE
maj 13 11:05:04 carrack systemd[1]: snap.workshop.workshopd.service: Failed with result 'exit-code'.
```

I can create LXD container of VM instances just fine. It seems like it's assuming that zfs is always available, and can used for storage which isn't true. If workshop is published through the snap store it should either try to support other systems where snapd can run or should include some sort of disclaimer that only Ubuntu is supported.

```
$ snap list workshop
Name Version Rev Tracking Publisher Notes
workshop 0.1.30-a8fb6ac3 126 latest/stable dlyfar classic
```