iotests: Add more "_require_drivers" checks to the shell-based tests

Test 051 should be skipped if nbd is not available, and 267 should
be skipped if copy-on-read is not enabled.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/051

@@ -41,6 +41,7 @@ _supported_proto file
 # A compat=0.10 image is created in this test which does not support anything
 # other than refcount_bits=16
 _unsupported_imgopts 'refcount_bits=\([^1]\|.\([^6]\|$\)\)'
+_require_drivers nbd
 
 do_run_qemu()
 {

tests/qemu-iotests/267

@@ -40,6 +40,7 @@ trap "_cleanup; exit \$status" 0 1 2 3 15
 _supported_fmt qcow2
 _supported_proto file
 _supported_os Linux
+_require_drivers copy-on-read
 
 # Internal snapshots are (currently) impossible with refcount_bits=1
 _unsupported_imgopts 'refcount_bits=1[^0-9]'