Fix dev setup due to not creating DB before tables

Summary:
Oops. The updated dev setup that I rushed out in the few minutes before launch
never actually worked! My bad. Sorry @andyzg that you ran into this, and thanks
for reporting.

Test Plan:
moved the db/rethinkdb_data directory; restarted local dev server;
ran `make ensure_tables_and_indices`; verified that that failed. Made fix; ran
the same recipe; ensured that worked.

Reviewers: xymostech, spicyj

Reviewed By: spicyj

Differential Revision: http://phabricator.benalpert.com/D208