libsnapshot: Fix vts_libsnapshot_test

Fix SnapshotUpdateTest.QueryStatusError which
was failing on targets where userspace-snapshots are not
yet enabled.

Bug: 224586316
Test: vts_libsnapshot_test -force_config dmsnap --gtest_filter=SnapshotUpdateTest.QueryStatusError
Signed-off-by: Akilesh Kailash <akailash@google.com>
Change-Id: Ibaacff9b03eafe0bfa537d0f9cab98b7caceb37e