Add jshint for javascript linting

Added nodeenv as a test requirement.

Added a jshint environment to tox.ini, which installs node.js into the
python virtual environment with nodeenv, installs jshint using npm,
and calls runtest.sh to run the tests.

runtest.sh now supports the -j|--jshint flags to run jshint on the
javascript files. jshint must be installed before running runtest.sh

The documentation also got updated to include some info about testing.

Change-Id: I3e7dcea481806eddc10625fe353ac9092b30573a
Partial-Bug: #1282961
Merge "Add jshint for javascript linting"