qemu-iotests: Do not execute 052 with -nocache

Test 052 uses qemu-io -s which will result in bdrv_open trying to create
a temporary snapshot file in /tmp. However, since O_DIRECT and tmpfs
do not work well together, disable this test for -nocache.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/052

@@ -41,6 +41,7 @@ trap "_cleanup; exit \$status" 0 1 2 3 15
 _supported_fmt generic
 _supported_proto generic
 _supported_os Linux
+_unsupported_qemu_io_options --nocache
 
 
 size=128M