Allow client specific redirect upon login server signup

A client_id is expected within login-server generated
expiring codes for signup.  This client is retrieved and
the SIGNUP_SUCCESS_REDIRECT_URL from the client's
additionalInformation hash is returned along with the new
user account info, for use by the login-server

[#73331674] https://www.pivotaltracker.com/story/show/73331674

Signed-off-by: Rob Gallagher <rgallagher@pivotallabs.com>
Allow bootstrapping signup-success-redirect-url

from oauth-clients.xml

[#73331674] https://www.pivotaltracker.com/story/show/73331674

Signed-off-by: Rob Gallagher <rgallagher@pivotallabs.com>
Change the app signup callback to be valid for test

[#73331674] https://www.pivotaltracker.com/story/show/73331674

Signed-off-by: Rob Gallagher <rgallagher@pivotallabs.com>
Merge branch 'feature/73331674-client_signup_redirect' into develop