test/py: add skip marker for reliance on tools

Some tests use external tools (executables) during their operation. Add
a test.py mark to indicate this. This allows those tests to be skipped if
the required tool is not present.

Signed-off-by: Stephen Warren <swarren@nvidia.com>

test/py/tests/test_vboot.py

@@ -31,6 +31,10 @@ import u_boot_utils as util
 
 @pytest.mark.boardspec('sandbox')
 @pytest.mark.buildconfigspec('fit_signature')
+@pytest.mark.requiredtool('dtc')
+@pytest.mark.requiredtool('fdtget')
+@pytest.mark.requiredtool('fdtput')
+@pytest.mark.requiredtool('openssl')
 def test_vboot(u_boot_console):
     """Test verified boot signing with mkimage and verification with 'bootm'.