snap: Support snap channels

Fixes #268
1 job for channels in 15 minutes and 16 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
failed #322411
build-gnome-software

00:15:16

 
Name Stage Failure
failed
build-gnome-software Build

Ok: 0
Expected Fail: 0
Fail: 1
Unexpected Pass: 0
Skipped: 0
Timeout: 0

ERROR: Job failed: exit code 1