Import dependencies to make unit tests friendlier to running independently

The HHVM test runner runs the unit tests in parallel. Currently some tests
fail because not all the dependencies are properly included.

This is similar to 840f7b12150aedca8f8d6d57c0da15dab9f99a07

Signed-off-by: Jeff Chan <jefftchan@gmail.com>
Merge pull request #1035 from jeffchan/fix-database-interface-tests

Import DatabaseInterface to make unit tests friendlier to running independently