This object allows to run the "stress" cmdline program in the background
on the specifies run_node, to simulate system load.
To run stress, a test can simply do:
stress = tenv.stress(epc.run_node())
stress.start(cpu_workers=2, mem_workers=1, io_workers=1)
And the test environment will remember to stop it when the test finishes.
Change-Id: I21023e6c64c48109f294291bfe3d8d8f4e1de038
