Skip test if a migration capability isn't available

If a test tries to use a migration capability that doesn't exist
in that version of QEMU or can't be used in combination with some
other setting then we'll get an exception.  Trap this exception
and cause the test to be skipped.
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>

qemu/tests/migration.py

@@ -10,6 +10,7 @@ from virttest import utils_misc
 from virttest import utils_test
 from virttest import utils_package
 from virttest import error_context
+from virttest import qemu_monitor     # For MonitorNotSupportedMigCapError
 
 
 @error_context.context_aware
@@ -217,13 +218,18 @@ def run(test, params, env):
                     logging.info("Round %s ping..." % str(i / 2))
                 else:
                     logging.info("Round %s pong..." % str(i / 2))
-                vm.migrate(mig_timeout, mig_protocol, mig_cancel_delay,
-                           offline, check,
-                           migration_exec_cmd_src=mig_exec_cmd_src,
-                           migration_exec_cmd_dst=mig_exec_cmd_dst,
-                           migrate_capabilities=capabilities,
-                           mig_inner_funcs=inner_funcs,
-                           env=env)
+                try:
+                    vm.migrate(mig_timeout, mig_protocol, mig_cancel_delay,
+                               offline, check,
+                               migration_exec_cmd_src=mig_exec_cmd_src,
+                               migration_exec_cmd_dst=mig_exec_cmd_dst,
+                               migrate_capabilities=capabilities,
+                               mig_inner_funcs=inner_funcs,
+                               env=env)
+                except qemu_monitor.MonitorNotSupportedMigCapError as e:
+                    test.cancel("Unable to access capability: %s" % e)
+                except:
+                    raise
 
             # Set deamon thread action to stop after migrate
             params["action"] = "stop"