fix(tests): add SRI testing to functional tests

[vladikoff]

Fixes #4364

@shane-tomlinson @vbudhram r?

[shane-tomlinson]

awesome!

[vbudhram]

@vladikoff Test works great when running local content-server in production mode. I reran the CI tests a couple of times and got the same error

× firefox on any platform - Firefox Desktop Sync v1 reset_password - reset password, verify different browser - from original tab's P.O.V. (6.648s) AssertionError: expected false to be true

I think these are unrelated, r+ unless you think otherwise.

[shane-tomlinson]

× firefox on any platform - Firefox Desktop Sync v1 reset_password - reset password, verify different browser - from original tab's P.O.V. (6.648s) AssertionError: expected false to be true

This is fixed by #4428, just need to rebase.