R1:cbde56cdce1a

Properly create xhpast database

Summary:
It isn't deleted by `storage destroy`.

This should be a no-op on current storage because we execute `CREATE DATABASE IF NOT EXISTS`.

Test Plan:
$ bin/storage destroy --dryrun

Reviewers: nh, epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3659