fix issues with yaml_server restart

Some issues were detected when trying to restart the yaml_server. We observed
that sometimes, when you try to restart the server, it wouldn't come back up.
Upon further investigation this seemed to be reproducible, when performing a
get request---using curl---immediately prior to attempting to restart the
server.  When looking at the log files, the following log message was observed
in syslog:

Mar  7 14:38:52 isdeblnwl081 yaml_server[23982]: CRITICAL: Could not start
server: [Errno 98] Address already in use

When using the google, the following stackoverflow post hinted at some
potential fixes:

http://stackoverflow.com/questions/15260558/python-tcpserver-address-already-in-use-but-i-close-the-server-and-i-use-allow

Implementing this fix, does solve problem, at least for the local test setup we
have.