[petsc-dev] best fix for -hosts localhost issue

[Geoffrey Irving]

I'd like to implement the right fix for the -hosts localhost issue.
Recall that the problem is passing "-hosts localhost" to mpiexec when
running tests.  Matt apparently needs it for his machine (Mac OS X),
and it is not allowed on mine (Ubuntu, OpenMPI).  Should we check for
the validity of -hosts and use it if so, or do we like Jed's grumpy
anti-Mac solution? :)

Geoffrey