Fixed MPI framework.

MPI did not run on Mesos due to broken version-dependent paths and
broken reg exp in python scheduler script that failed to extract
ip and port of mpd processes. Corrected the above.

(An effort is underway to support the hydra process management
 facility in lieu of the deprecated mpd...)

From: Bernd Mathiske <bernd@mesosphere.io>
Review: https://reviews.apache.org/r/17635
Adds Medidata Solutions to 'Powered by Mesos' list.
Fixed a compilation issue in Subprocess.