Relax assertion in test_get_all_shards

when listing all shards, currently test expects to find only shards
that it has just created, but there could be other, pre-existing shards,
like default "None" one aor shards created by other tests
running in parallel.

Instead, check that the created shards is a subset of all shards.

Closes-Issue: PRODX-56216
Change-Id: Ic35f9be232837922ae8ed857c7ea0bb58e064987
1 file changed