Some tests using MPI fail due to insufficient number of slots

Created by: keichi

These tests fail on my laptop with the recent version of ADIOS2:

The following tests FAILED:
	  1 - HeatTransfer.BPFile.Write.MxM (Failed)
	  2 - HeatTransfer.BPFile.Read.MxM (Failed)
	  3 - HeatTransfer.BPFile.Dump.MxM (Failed)
	  4 - HeatTransfer.BPFile.Validate.MxM (Failed)
	  5 - HeatTransfer.BPFile.Write.MxN (Failed)
	  6 - HeatTransfer.BPFile.Read.MxN (Failed)
	  7 - HeatTransfer.BPFile.Dump.MxN (Failed)
	  8 - HeatTransfer.BPFile.Validate.MxN (Failed)
	  9 - HeatTransfer.BPFile.Write.Mx1 (Failed)
	 10 - HeatTransfer.BPFile.Read.Mx1 (Failed)
	 11 - HeatTransfer.BPFile.Dump.Mx1 (Failed)
	 12 - HeatTransfer.BPFile.Validate.Mx1 (Failed)
	 13 - HeatTransfer.SST.MxM (Failed)
	 14 - HeatTransfer.SST.Dump.MxM (Failed)
	 15 - HeatTransfer.SST.Validate.MxM (Failed)
	 16 - HeatTransfer.SST.MxN (Failed)
	 17 - HeatTransfer.SST.Dump.MxN (Failed)
	 18 - HeatTransfer.SST.Validate.MxN (Failed)
	 19 - HeatTransfer.SST.Mx1 (Failed)
	 20 - HeatTransfer.SST.Dump.Mx1 (Failed)
	 21 - HeatTransfer.SST.Validate.Mx1 (Failed)
	 22 - HeatTransfer.InsituMPI.MxM (Failed)
	 23 - HeatTransfer.InsituMPI.Dump.MxM (Failed)
	 24 - HeatTransfer.InsituMPI.Validate.MxM (Failed)
	 25 - HeatTransfer.InsituMPI.MxN (Failed)
	 26 - HeatTransfer.InsituMPI.Dump.MxN (Failed)
	 27 - HeatTransfer.InsituMPI.Validate.MxN (Failed)
	 28 - HeatTransfer.InsituMPI.Mx1 (Failed)
	 29 - HeatTransfer.InsituMPI.Dump.Mx1 (Failed)
	 30 - HeatTransfer.InsituMPI.Validate.Mx1 (Failed)
	111 - ADIOSSstTest.3x5 (Failed)
	112 - ADIOSSstTest.3x5BP (Failed)
	113 - ADIOSSstTest.5x3 (Failed)
	118 - ADIOSSstTest.FtoC_3x5 (Failed)
	119 - ADIOSSstTest.FtoC_3x5BP (Failed)
	120 - ADIOSSstTest.CtoF_3x5 (Failed)
	121 - ADIOSSstTest.FtoF_3x5 (Failed)
	122 - ADIOSSstDelayedReaderTest.3x5 (Failed)
	123 - ADIOSSstDelayedReaderWithBlockingTest.3x5 (Failed)

Error message:

1: --------------------------------------------------------------------------
1: There are not enough slots available in the system to satisfy the 4 slots
1: that were requested by the application:
1:   /Users/keichi/Projects/research/ADIOS2/build/bin/heatTransfer_write_adios2
1:
1: Either request fewer slots for your application, or make more slots available
1: for use.
1: --------------------------------------------------------------------------

A workarounds that I found is to edit the cmake file (e.g. examples/heatTransfer/TestBPFileMx1.cmake) and reduce the number of requested MPI processes or add the --oversubscribe flag.

ADIOS2 4c6e11f7
MPI: Open MPI 3.1.1
OS: macOS 10.13.4 (17E202)
CPU: 2.3 GHz Intel Core i5 (2 cores, 4 threads)

Thanks.