Code review comment for bootstack-ops:mtu-scripts

Thanks for checking this out Peter - I've added capture of return code and stdout and stderr for failed pings, and print a summary at the end of the check-mtus script, for better feedback when diagnosing MTU issues.

I stuck with standard ping though, as I'd like to avoid needing to install fping to run this script. I also found some inconsistencies in it's output when pinging hosts with incorrect MTUs that made it a lot harder to get good status information out of it. It was dumping a failure for every host, whilst simultaneously dumping success messages to stdout for the OK hosts.