only disable SquashFS if it's not needed

Ubuntu Snaps need SquashFS so we cannot disable it easily. Instead we
check for running Snap Service.

Signed-off-by: Martin Schurz <Martin.Schurz@t-systems.com>

Author: schurzi

controls/os_spec.rb

@@ -254,7 +254,10 @@
     its(:content) { should match 'install jffs2 /bin/true' }
     its(:content) { should match 'install hfs /bin/true' }
     its(:content) { should match 'install hfsplus /bin/true' }
-    its(:content) { should match 'install squashfs /bin/true' }
+    # Ubuntu Snaps need SquashFS to function
+    unless service('snapd').running?
+      its(:content) { should match 'install squashfs /bin/true' }
+    end
     its(:content) { should match 'install udf /bin/true' }
     # if efi is active, do not disable vfat. otherwise the system
     # won't boot anymore