Rebased serialize configuration.

This includes the configuration serialization updates.

NOTE: We've s/mapred.mesos.executor/mapred.mesos.executor.uri/ to be more explicit and also because we added mapred.mesos.executor.command and mapred.mesos.executor.directory for more control.

Also, blame @florianleibert for random code motion here, he uses an IDE which apparently is opinionated about where some code belongs. ;)