Fix tests with MySQL 5.7.9

[luizpvas]

From MySQL's reference manual:

NO_AUTO_CREATE_USER will be removed in a future MySQL release, at which point its effect will be enabled at all times (GRANT will not create accounts).

This pull request makes all tests pass against MySQL 5.7.9.

I was getting the following error before the changes:

luiz@asus:~/Code/Go/src/github.com/refl/mysql$ go test github.com/refl/mysql
--- FAIL: TestStrict (0.02s)
    driver_test.go:116: Error on Exec CREATE TABLE test (a TINYINT NOT NULL, b CHAR(4)): Warning 3090: Changing sql mode 'NO_AUTO_CREATE_USER' is deprecated. It will be removed in a future release.
--- FAIL: TestSqlInjection (2.30s)
    driver_test.go:116: Error on Exec CREATE TABLE test (v INTEGER): Warning 3090: Changing sql mode 'NO_AUTO_CREATE_USER' is deprecated. It will be removed in a future release.
--- FAIL: TestInsertRetrieveEscapedData (1.71s)
    driver_test.go:116: Error on Exec CREATE TABLE test (v VARCHAR(255)): Warning 3090: Changing sql mode 'NO_AUTO_CREATE_USER' is deprecated. It will be removed in a future release.
FAIL
FAIL    github.com/refl/mysql    43.664s