Do not ask for a password for users signing into a non-key
requesting RP if they already have an FxA session of any sort.
I removed a lot of tests that now seem duplicate, since there is
no real distinction between a "Sync" signin and an "OAuth" signin
when it comes to whether to display the password field.
I also added onto a bunch of the "cached session" tests
to actually click the "submit" button to ensure the user
is redirected where they are supposed to be. The idea
is to follow on with trying expired cached credentials
targeting the problems uncovered in #999.
fixes#1371
Shane Tomlinson