tests: add check that removal of snaps works with user data

[NucciTheBoss]

Test adds check to see if https://bugs.launchpad.net/snapd/+bug/2002697 is easily reproducible when using home directories exported via NFSv3 or NFSv4.

This issue is easily reproducible on HPC deployments where NFS is used as the shared filesystem for exporting data across the cluster. Snaps can be installed and used by "remote users" - defined in LDAP and not in /etc/passwd - but they cannot be refreshed an/or removed when root_squash is enabled as snapshotting SNAP_USER_DATA and SNAP_USER_COMMON is disallowed by the filesystem.