iotests: Check whether luks works

Whenever running an iotest for the luks format, we should check whether
luks actually really works.

Tests that try to create luks-encrypted qcow2 images should do the same.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200625125548.870061-7-mreitz@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
diff --git a/tests/qemu-iotests/188 b/tests/qemu-iotests/188
index 09b9b60..13b225f 100755
--- a/tests/qemu-iotests/188
+++ b/tests/qemu-iotests/188
@@ -39,6 +39,7 @@
 _supported_fmt qcow2
 _supported_proto generic
 _supported_os Linux
+_require_working_luks
 
 
 size=16M