[test] Adapt MCH checks to CrayPE 17.06 on Kesch (RH7.5)

[lucamar]

I have tested the MCH checks using the Cray Programming Environment 17.06 (module PE/17.06) and the MPI library openmpi/4.0.1-pgi-18.5-gcc-5.4.0-2.26-cuda-8.0.61 for PrgEnv-pgi/18.5.
The latter is not yet in production, since is part of the pull request eth-cscs/production#1271, therefore I had to use my sandbox for testing it.
Fieldextra checks cannot work at present since the module fieldextra/12.7.5-gmvolf-17.02 is not yet in production.

[lucamar]

I have updated the reference value of CudaStressTest, since it was failing occasionally.
The change is from 2.12769 to 2.25, an increase of ~ 5.7%.

[lucamar]

The failure of the checks HaloExchangeTest_nocomp and HaloExchangeTest_default on 144 MPI tasks (9 nodes) is unusual...

[vkarak]

@lucamar I see very bad performance for the HaloExchangeTest_default test. Is this expected?

Reason: performance error: failed to meet reference: elapsed_time=30.3839, expected 5.53777 (l=-inf, u=6.3684354999999995)

[lucamar]

@lucamar I see very bad performance for the HaloExchangeTest_default test. Is this expected?

Reason: performance error: failed to meet reference: elapsed_time=30.3839, expected 5.53777 (l=-inf, u=6.3684354999999995)

Unfortunately it was not happening so often in the past: we will need to monitor the check once we merge it.

[vkarak]

lgtm. Thanks @lucamar