Improve Default BaseDSN field in MySQBackendConfig

[shawnHartsell]

When setting up the setting up the defaults for the MySQLBackendConfig. If a BaseDSN is not supplied by a called then it will default to this structure:

fmt.Sprintf("%s:%s@tcp(%s:%d)/?parseTime=true", m.User, m.Password, m.Host, m.Port)

This DSN is missing a few critical items:

• database name: if this field is missing then a lock can't be required if the database server becomes unavailable
• timeouts: not having a timeout defined means that calls can wait forever. This is exacerbated if the issue occurs during the master heartbeat

[changsongl]

I have same issue with database name bug.
“failed to acquire lock while becoming master: failed to fetch current master state: Error 1046: No database selected”

Right now, I just use my own DSN instead of giving all mysql connection parameters. And I also fix the timeout problems by passing BaseDSN.