Check MySQL connection at startup
Check MySQL connection at startup

`sql.Open()` does not open any connections until the database is used
the first time. As result, `sql.Open()` does not return an error if
the server is not available, neither if DSN is not correct.

Signed-off-by: Fong-Wan Chau <e274eeff768c6396088ec6eb091f4bf4d47ab1e0@fongwanchau.com>

OpenHDX/web-api