cmd/migratedb: import hapg driver
cmd/migratedb: import hapg driver

Fix bug where migratedb would fail trying to use unrecognized
SQL driver.

Closes chain/chainprv#1509.
Reviewers: da39a3ee5e6b4b0d3255bfef95601890afd80709@kr



chain/chain,chain/chain,chain/chain,chain/chain,chain/chain,chain/chain