feat(tests): update user-agent in functional tests

[vladikoff]

v40 is pretty old!

[vladikoff]

so with this, a bunch of functional tests go crazy because fxaStatus actually starts sending a logged in account data (from the browser).

@shane-tomlinson we need to sit down and figure this one out probably...

[shane-tomlinson]

@vladikoff - you are right, this is going to wreck havoc. We could update the openPage listener to automatically listen for and respond to the fxaccounts:fxa_status event if no listener has already been defined, hopefully only a few tests would need to be updated then.

[shane-tomlinson]

We've gotta fix all those failures before merging! I think we should be able to do that by adding a default WebChannel listener that responds to fxaccounts:fxa_status. If no listener is added by the test for the message when calling openPage, add one.

[shane-tomlinson]

There is more here, while I was running the functional tests the fxaccounts:login message needs to be handled in many cases too, the browser was actually signing in!

[vladikoff]

filed https://github.com/mozilla/fxa-content-server/issues/7012