This updates the aws driver to use the statemachine framework which
should be able to scale to a much higher number of parallel operations
than the standard thread-per-node model. It is also simpler and
easier to maintain. Several new features are added to bring it to
parity with other drivers.
The unit tests are changed minimally so that they continue to serve
as regression tests for the new framework. Following changes will
revise the tests and add new tests for the additional functionality.
Change-Id: I8968667f927c82641460debeccd04e0511eb86a9
43678bf4c1