refactor(tests): Reduce boilerplate in the settings functional tests.
refactor(tests): Reduce boilerplate in the settings functional tests.

The settings functional tests did a lot of boilerplate setup to
open pages and fill in the sign in form. We have helpers for those.

swatilk/fxa-content-server,npestana/fxa-content-server,vladikoff/fxa-content-server,mozilla/fxa-content-server,shane-tomlinson/fxa-content-server,swatilk/fxa-content-server,shane-tomlinson/fxa-content-server,swatilk/fxa-content-server,shane-tomlinson/fxa-content-server,mozilla/fxa-content-server,vladikoff/fxa-content-server,npestana/fxa-content-server,npestana/fxa-content-server,vladikoff/fxa-content-server,mozilla/fxa-content-server