Added -b/--spot_bid option to clout script.

Still need to implement this functionality.
Added implementation for spot bidding.

Also added unit tests.
Updated documentation and examples.
Now uses --force-spot-master.

Also updated documentation to state units for spot bids and added sanity checking (includes new option --suppress_spot_bid_check).
Merge pull request #25 from jrrideout/issue_17

Added ability to use spot instances.