Set config doesn't propagate to internal variables or write to config file.

[benirose]

When changing a root level config setting, only the internal ummon.config variable is changed. Deeper properties that get set from the config on ummon start up (such as ummon.MAX_WORKERS) are not affected.

Additionally, the changes don't get written out to a config file, so restarting ummon won't load in the new settings.