Some Tests perform significantly worse on OpenMP

When we look at the performance of our tests across the different devices we see that OpenMP has some outliers ( https://open.cdash.org/viewTest.php?onlypassed&buildid=5485109 ).

ParticleAdvection:
 OPENMP - 30s
 SERIAL - 4s
 TBB    - 4s

ContourTree
 OPENMP - 26s
 SERIAL - 810ms
 TBB    - 210ms