Eliminate redundant IP address messages from failover monitor log

The failover monitor log has contained thousands of unnecessary messages saying an IP address is resolved to itself. This merge request eliminates such messages. It resolves issue #373.

Tests were performed with a modified scripts/failover-mon/check-failover.sh script that generated a failovermonCvmfs.log file. After the code change, the log shrunk by tens of thousands of lines since the unneeded entries were eliminated while its other contents were retained.