fix logging of (supposedly) "CRITICAL" condition

if it's "CRITICAL", it most probably better be LOG.error() instead info,
and it would REALLY help to have the cause included; see also
KengoTODA/findbugs-slf4j#74.

actually, perhaps this really should re-throw... let me propose that in
a follow-up change, and we can discuss if there is any reason to only go
half the way or merge both steps.

Change-Id: Ie824d8e8b1155c6bfd604dd83da2969c4d9cdb33
Signed-off-by: Michael Vorburger <vorburger@redhat.com>

diagstatus/api/src/main/java/org/opendaylight/infrautils/diagstatus/MBeanUtils.java

@@ -134,7 +134,7 @@ public static Object invokeMBeanFunction(String objName, String functionName) {
             MBeanServer mplatformMbeanServer = ManagementFactory.getPlatformMBeanServer();
             udpated = mplatformMbeanServer.invoke(objectName, functionName, null, null);
         } catch (InstanceNotFoundException | MBeanException | ReflectionException | MalformedObjectNameException t) {
-            LOG.info("CRITICAL : Exception in executing MBean function");
+            LOG.error("CRITICAL : Exception in executing MBean function", t);
         }
         return udpated;
     }
@@ -148,7 +148,7 @@ public static Object readMBeanAttribute(String objName, String attribute) {
             attributeObj = platformMbeanServer.getAttribute(objectName, attribute);
         } catch (AttributeNotFoundException | InstanceNotFoundException | MBeanException
                 | ReflectionException | MalformedObjectNameException t) {
-            LOG.info("CRITICAL : Exception in executing MXBean function");
+            LOG.error("CRITICAL : Exception in executing MXBean function", t);
         }
         return attributeObj;
     }