[OMPT,tests] Fix taskloop testcase scheduling effects

The taskloop testcase had scheduling effects. Tasks of the taskloop would
sometimes be scheduled before all task were created. The testing is now
split into two phases. First, the task creation on the master is tested,
than the scheduling events of the tasks are tested. Thus, the order of
creation and scheduling events is irrelavant.

Patch by Simon Convent

Reviewed by: protze.joachim, Hahnfeld

Subscribers: openmp-commits

Differential Revision: https://reviews.llvm.org/D50140

llvm-svn: 338580