(TK-92) Add graceful-shutdown support

Add graceful-shutdown support to the Jetty9 Webservice. Now,
when the webserver is shutdown, the server will give open
requests a chance to resolve themselves. Allow user to
configure the graceful shutdown stop timeout.
fyi, here's the code in Jetty that reads the stopTimeout: https://github.com/eclipse/jetty.project/blob/master/jetty-server/src/main/java/org/eclipse/jetty/server/Server.java#L415.  I read this as the Server class does not wait for shutdowns if stopTimeout is set to 0 at stop time.