Create a better error message for those logging in with secondary e-mail (Google login) (BB-15815)

With Google login accounts we're running into an error when logging in: If a user has two e-mail addresses on their account, and the secondary is not primary we'll return an ambiguous '500 error' when they try to login:

1. Have an account with two e-mail addresses, non-primary attached to a Google account
2. User logins in with non-primary e-mail and they get the following:

#!python

We noticed that
there is an existing Bitbucket account associated with your email address.
Log in to connect it with Google!

If this is done, and user logins in with non-primary e-mail, the user will receive a "Something went wrong" and then they'll go back and be logged in as primary e-mail address. We should return an error a little less ambiguous.. possibly "Please sign-in with your primary e-mail address"