Changes

Set sched RR Priority on main thread

Since we are still affected by Python GIL, it makes sense to also set
the main thread (which is actually also expected to be real time) to a
real time priority.

Use a slightly higher rr prio (prio + 1) to the clckgen thread.

Change-Id: I6aa22125e7de4f472d691b271639d5bee25762cb