change HSS to use SQLite

[spencersevilla]

A significant part of our setup/deployment process is installing/configing MySQL, setting up user/group/db, installing a "test" db so that the EPC boots after install, etc. All of these headaches can be avoided by migrating over to SQLite which just uses a file instead :-). This has minor implications for write-heavy operations but AFAIK our HSS just reads the DB, and DB operations are very few and far between (e.g. create a new user).