Allow users to choose which phantomjs they use

[ivanistheone]

Description

I ran into problems while running https://github.com/learningequality/sushi-chef-teachengineering
because phantomjs version on vader is 1.9.x
but chef script depends on phanomjs 2.1.x

Workararound

Download phantomjs2.1.1 to chef dir

cd /data/sushi-chef-teachengineering
wget https://bitbucket.org/ariya/phantomjs/downloads/phantomjs-2.1.1-linux-x86_64.tar.bz2
tar xvjf phantomjs-2.1.1-linux-x86_64.tar.bz2

then monkey patched venv/lib/python3.5/site-packages/ricecooker/utils/downloader.py from

    try:
        if loadjs:                                              # Wait until js loads then return contents
            driver = driver or webdriver.PhantomJS()

to

    try:
        if loadjs:                                              # Wait until js loads then return contents
            driver = driver or webdriver.PhantomJS('/data/sushi-chef-teachengineering/phantomjs-2.1.1-linux-x86_64/bin/phantomjs')

Feature spec

Ricecooker utils downloader could use environement variable like PHANTOM_JS_BINARY to optionally specify a particular binary we want to use.

[ivanistheone]

Fixed in #144