improved PME load balancing reporting

With the group cut-off scheme, rlist was reported incorrectly.
Added a note in log and stderr when PME load balancing increases
the non-bonded workload by more than 50%.

Change-Id: I7d46f5a110b24cbb40b6b9cb53a1d90715c7c5ec
Merge "improved PME load balancing reporting" into release-4-6