New v6/v7 tomcat server.xml configuration fetching and editing...

Now put the fetching and editing code for tomcat v7 (and v6)
server.xml file in the main line of execution during setup_tomcat.

Caveat:
There are now two places where this behavior happens.
Now in the usual tomcat_config() function, but also stand-alone in the
migrate_tomcat_credentials_to_esgf() function.
Be aware...
TODO - consolidate into a single function...