Fix VM load release in Heat autoscaling tests

Make load release command more targeted in killing a CPU loading process
by getting its actual PID.

The exact implementation in two ssh commands is due to pecularities of
bash in Fedora 17 used as image for VMs in autoscaling test.

Change-Id: I9e0b67bffa7a944241f1e15ed92e29b0b6e040dd
Related-Bug: #1361629
Merge "Fix VM load release in Heat autoscaling tests"