PyWren runtime builders

To build all the runtimes in runtimes.py on the aws machine builder and put them on the staging server:

fab -f fabfile_builder.py -R builder build_all_runtimes 

To test, push the repo to github, which will trigger a travis build pointing at the staged runtimes.

To deploy them and shard them, do this:

fab -f fabfile_builder.py -R builder deploy_runtimes:num_shards=50