Fix FrameworksServicesTests:PrioritySchedulingTest.

1. Make sure the test schedules enough jobs that preemption becomes a
possibility.
2. Use a priority that won't be overriden (increased) when the jobs
start running.

Bug: 146570600
Test: atest FrameworksServicesTests:PrioritySchedulingTest
Change-Id: Ib1680091947998c3d6a1d9414a0c79bd6b4e0f96
1 file changed