Changed psutil dep. to match global requirements

Global requirements now expect that psutil<2.0.0
Therefore the call to children() in psutil was
invalid and was failing tests, so this commit
changes the call to get_children() and updates
test-requirements to reflect this version change

Change-Id: I9570dd1ec0cb9fd7efaee292d7996510b56ab611
Merge "Changed psutil dep. to match global requirements"