[REF] tests: replace phantomjs by Chrome headless

As the phantomjs project was suspended[1], there was a need to change the js test
engine. Moreover, the engine was rather old and leading to non
deterministic crashes.

Chrome headless was choosen for simplicity and the long term vision of
the devtools protocol [2].

The 'phantom_js' method still exists but will be deprecated in
favor of 'browser_js' with the same parameters.

In order to communicate with the browser, the python websocket-client package
is needed.

[1] ariya/phantomjs#15344
[2] https://chromedevtools.github.io/devtools-protocol/