add debug logs when access checkers fail to find API

When the access checkers fail for api discovery, we fail silently.
instead record a debug message.

Signed-off-by: Prasanna Santhanam <tsp@apache.org>

plugins/api/discovery/src/org/apache/cloudstack/discovery/ApiDiscoveryServiceImpl.java

@@ -219,6 +219,7 @@ public class ApiDiscoveryServiceImpl implements ApiDiscoveryService {
                 try {
                     apiChecker.checkAccess(user, name);
                 } catch (Exception ex) {
+                    s_logger.debug("API discovery access check failed for " + name + " with " + ex.getMessage());
                     return null;
                 }
             }