tests: latency_measure: Update context switch

Updates both the preemptive and cooperative thread context switch
benchmark tests so that not only will they share the same
infrastructure, but they can both get the context switch times
when switching from ...
  1. Kernel thread to kernel thread
  2. Kernel thread to user thread
  3. User thread to kernel thread
  4. User thread to user thread

Signed-off-by: Peter Mitsis <peter.mitsis@intel.com>