TEST: Key invalidation

Test the key invalidation functionality.

Signed-off-by: David Howells <dhowells@redhat.com>
TEST: Check depth of tree output by "keyctl show"

Check depth of tree output by "keyctl show" to make sure it shows the full
depth and not an abbreviated tree.

Also, whilst we're at it, check that we can show the contents of a nominated
keyring.

Signed-off-by: David Howells <dhowells@redhat.com>