ConnectionPoolMBeanManager does not log stacktrace on error.

[marccarre]

This potentially prevents from diagnosing the root cause of the error.

See also: https://github.com/Netflix/astyanax/blob/master/astyanax-core/src/main/java/com/netflix/astyanax/connectionpool/impl/ConnectionPoolMBeanManager.java

Lines 60-63 in registerMonitor:

catch (Exception e) {
    LOG.error(e.getMessage());
    monitors.remove(monitorName);
}

Lines 73-75 in unregisterMonitor:

catch (Exception e) {
    LOG.error(e.getMessage());
}