Honor job exclusive with reserved cores

If job requests --exclusive then do not use nodes which have any cores in an
advanced reservation. Previously the job would be allocated all of the cores
outside of the advanced reservation.
select/cons_res log change

Disable some logging that would be very slow unless
the _DEBUG flag is set in the plugin
Fix job --exclusive option enforcement

If job requests --exclusive then do not use nodes which have any cores in an
advanced reservation. Also prevents case where nodes can be shared by other
jobs.