optimize darshan startup routines
Darshan scans mount points and collects information about them at startup. In the past we were forced to do this on every process in order to correctly match files to mount points at run time. This is no longer necessary, however.
We should eliminate the logic that collects device ids from each mount points. We should also modify the algorithm that collects the remaining information (mount point path and default block size) so that it is only collected at rank 0 and then broadcasted to ranks 1 through N-1.