Change base image to sitespeed.io image

[krompaco]

See this as a proposal.

I've been testing it for a couple of weeks as I think there would be some benefits to use the sitespeedio/sitespeed.io image instead of their webbrowsers image.

1. Same version number as the npm package
2. Opens up possibility to run tests with the internal command used by sitespeedio's image instead of using the script from npm install (requires some IF-statements in the sitespeed-based tests but could improve stability and lean more on the great work from them)

Not a big change. The additions are mainly to avoid conflicts and to use same aliases as their image does.

[7h3Rabbit]

@krompaco just an update, the reason for the delay is that I want to test this setup in great depth. so far haven't had time to setup a docker environment but will hopefully happens soon.

[7h3Rabbit]

@krompaco This is what I want to test in depth:

• Is it possible to remove the sitespeed specifict npm install?
• Do everything work? (test with all test against all sites at webperf.se)
• Are there any big benefits of changing parent docker image? Some searchresults indicate better hardware support.
• Is anything missing in the Docker image (if so, can we fix it/give instructions for it?)
• Document use of Docker (read: get a better understanding of docker)
• See if -it and -cap-add=SYS_ADMIN can be removed (SYS_ADMIN is dangerous according to a few searchresults)
• See if there are any benefit of the windows specific ps1 files
• wait for #488 so it can be tested at the same time.

If you (or someone else) can help answer above that would be very helpful 😄