use opal atomics to modify ompi initialize/finalize related variables

[hppritcha]

By using opal atomics to modify/read the following ompi initialize/finalize related variables:

ompi_mpi_init_started
ompi_mpi_initialized
ompi_mpi_finalized 
ompi_rte_initialized
ompi_mpi_finalize_started

would help in bringing some MPI query functions into compliance with the MPI-3 specification.

See issue #493.

[jsquyres]

Per #1007, I'm not sure that this a correct premise any more (i.e., using a mutex was easier than using atomics). Regardless, I think that this ticket is subsumed by #1007, so I'll close this one.