Unified Test Runner

Summary: this adds a single command that can be used to run all tests and receive a single result, both in the VM and in TravisCI

Test Plan:
run `bin/tests` to install the prereqs and run all the tests

run `bin/tests help` to see the command usage

run `bin/tests install` to install the prereqs then `bin/tests run --no-install` to run without installing (which is what TravisCI will do using `before_script` & `script`)

try running from any current working directory... the script should work from anywhere

I tried using https://github.com/jolicode/JoliCi to test the travis script, but couldn't get it to run properly. Both travis commands work when tested locally, and the exit codes are correct, so the travis build should work but will need to be tested live.

Reviewers: rjmackay, vladimir, shadowhand

Reviewed By: shadowhand

Differential Revision: https://phabricator.ushahidi.com/D459