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

tests/qemu-iotests/048

@@ -46,7 +46,7 @@ _compare()
 . ./common.filter
 . ./common.pattern
 
-_supported_fmt raw qcow qcow2 qed luks
+_supported_fmt raw qcow2 qed luks
 _supported_proto file
 _supported_os Linux