Loadtracking.py: Cgroups test userspace freezing update
Created by: Elieva
The class _PELTTaskGroupsTest(LisaTest) has been updated to freeze the userspace as expected by the new syntax. Namely, the userspace is freezed in a "with" statement to catch error and unfreeze correctly in this case.
Signed-off-by: Elieva Pignat Elieva.Pignat@arm.com