cs.AuthMechanismProperties is not initialized when mechanism set by --authenticationMechanism

Inside this block in setOptionsFromURI():

if opts.Kerberos.Service != "" && !cs.AuthMechanismPropertiesSet {

    cs.AuthMechanismProperties["SERVICE_NAME"] = opts.Kerberos.Service

    cs.AuthMechanismPropertiesSet = true        

}

cs.AuthMechanismProperties is not initialized if the auth mechanism was not specified in the URI (i.e. it didn't get initialized during connstring.Parse()).

We need to do the same thing that we do for the mongodb-aws mechanism and add this to the start of the block:

if cs.AuthMechanismProperties == nil {

    cs.AuthMechanismProperties = make(map[string]string)

}