Only log console log if nova supports consoles

If a scenario test fails during ssh the standard procedure is to log
the console for the server. However, this can only be done if nova
supports consoles. This commit adds a check to see if nova supports
getting the console for a server before it attempts to do it.
Otherwise if nova doesn't support getting the console and an ssh
connection fails the test will fail on getting a console and not the
ssh connection. It looks like this check wasn't added during the
scenario test port to the tempest clients.

Change-Id: I681b3065d86cd31837a9ef5d91d25847fa47a8f4
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index f7db79d..68957db 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -398,6 +398,9 @@
         LOG.debug("image:%s" % self.image)
 
     def _log_console_output(self, servers=None):
+        if not CONF.compute_feature_enabled.console_output:
+            LOG.debug('Console output not supported, cannot log')
+            return
         if not servers:
             _, servers = self.servers_client.list_servers()
             servers = servers['servers']