iotests: skip 048 with qcow which doesn't support resize

Test 048 is designed to verify data preservation during an
image resize. The qcow (v1) format impl has never supported
resize so always fails.

Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20170623162419.26068-7-berrange@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
