README improvements
Work towards adding a new Stress Test runner

The Stress Test runner is similar to the soak test runner in that it
simulates continuous load on the system but it differs from stress
testing in that it gradually increases the load on the system over the
time.  The current implementation has some bugs that still need to be
ironed out
Improve how stress testing ramp up is implemented

This improves the implementation of the StressTestParallelClientManager
so that the ramp up is much more controlled and consistent
Minor tweaks to Stress Testing implementation
Fix non-halt when sanity checks failed

This commit fixes a bug present in all the runners which causes them to
not actually halt execution when sanity checks fail in some
circumstances.  It was also found that the behaviour across the runners
was not consistent so the relevant code was refactored out into a
protected method in AbstractRunner and the derived runners all changed
to call the same helper method.

This runSanityChecks() method will see if sanity checks are enabled, if
so try to run them and if the necessary sanity checking level is not met
asks the runner to halt
Fix logic error in checkSanity()

A bug was spotted in checkSanity() by Vamsikrishna Annem regarding the
running of sanity checks.  The bug meant that runners weren't actually
checking for failed operations correctly so the sanity checks were
always reported as passing regardless of the actual status of the
operation.

This commit improves the logic to check that the operation was actually
successful and only report successful operations as passing sanity
checks