Updates to mrfgen in support of HLS.  Mainly some tweaks to _not_ delete VRT files that are in the work directory.
Updates to mrfgen in support of HLS.  Mainly some tweaks to _not_ delete VRT files that are in the work directory.

nasa-gibs/onearth,nasa-gibs/onearth,nasa-gibs/onearth,nasa-gibs/onearth,nasa-gibs/onearth,nasa-gibs/onearth