The previous safe_system() is quite thorough, but much more than we
really need in this script. Use a far simpler version that is
significantly easier to maintain.
Also log some of the critical steps that a human can examine the
output upon a failure (e.g., when the failure happens when launched
via cron).
Finally, set the version number to not include "openmpi-", because
Coverity has a limited-width display of the version number.
Move the openmpi-nightly-coverity.pl script into the directory where
all the other build server scripts live.
Leave the coverity-model.c file in the coverity dir, because it's
specific to coverity. Other items can be added into the
coverity-model.c, if helpful (and then we can re-submit that model
file).
