Add user data test cases to the common domain data.

[lgarron]

We currently have a /mixed folder that works on every domain.
Chromium needs a bunch of test cases, and this approach scales better than making a new subdomain every time. Also allows testing combined downgrade conditions (e.g. SHA-1 with password).

Strawman:

• Add a user-data (maybe user-data-input) folder into common
• Modify common.conf to serve that dir (similar to /mixed).
• Add cases. Each case is a folder with an index.html file (and possible any resources that are specific to the case).

[lgarron]

@marumari, sound okay?

(@ericlaw1979 is working on these tests cases, so I want to make sure we send him on the right path.)