travis testing

Adds individual tests for each command in `checks` against aws cli 1.3.x and 1.5.x.

- [x] Figure out how to unhardcode net device eth0 in netin/netout
- [x] Fix checks on aws cli 1.5.x
Refactored such that `prev` is always set -- on first run (before a baseline value has been established in `/tmp/cwput_rx_bytes`) the value will be 0.