If a modify operation does not specify our attribute then we need to short
circuit the loop, otherwise on enforcing we will return an error by mistake if
we are not Directory Manager because generate is false if the attr is not
found.
By setting the enforce flag in the configuration we prevent anyone from storing
arbitrary values and allow only Directory Manager to override the plugin.
Users can only set the value to the magic value (usually 0) to have the uuid
regenerated, and nothing else.
Remove one level of indentation from the main function by jumping
to the end immediately if the configuration list is empty.
Other minor style cleanups.
