Db test config (#43)

* Allow tests to specify mysql connection info.

User can set MYSQL_TEST_USER, MYSQL_TEST_PASS and MYSQL_TEST_HOST
environment variables for test environments that need that.

* Changes from testing.

Need to set both time fields as '0000-00-00' depends on a feature
deprecated in MySQL 5.7.4.

Go lint wanted snake case for my sql_config var. sqlConfig it is.

* Go go idioms.

Based on feedback from Niall, a cleaner way to do this in Go.