Fixed the MPI recognition string in g_tune_pme

Since the identifying string "NNODES="is not printed any more by MPI-enabled
mdrun, we now use the "MPI library:" string instead.

Change-Id: Ibbcc0678a7c89057743129aa664fad8bb68f1941
Fix code bug with thread-MPI on PowerPC with xlc

Change-Id: I8254ae915fdd24e02cf8f07789c69c3d4b35525e
Merge "Fixed the MPI recognition string in g_tune_pme" into release-4-6
Merge "Fix code bug with thread-MPI on PowerPC with xlc" into release-4-6