VM files may be already removed. Don't fail on this while removing a
VM, it's probably the reason why domain is being removed.
qvm-remove tool have its own guard for this, but it isn't enough - if
rmtree(dir_path) fails, storage.remove() would not be called, so
non-file storages would not be cleaned up.
This is also needed to correctly handle template reinstallation - where
VM directory is moved away to call create_on_disk again.
QubesOS/qubes-issues#2412
1418555346