Ensure shared db is created by server.

* Also remove unneeded need_auth() method (because all requests need auth).
* This closes #2491.
Fix tests paths.
Prevent Twisted==12.0.0 from messing with OpenSSL.
Remove non-token auth schemes.

* Closes #2371.
Merge remote-tracking branch 'drebs/feature/2491-soledad-server-create-the-shared-database-in-couch' into develop