Mailconnector transports issue460

This commit will resolve the issue #460 regarding using single or multiple transports within the config file.  I have tested with the existing mocha tests and all are passing.  This PR does not resolve issue https://github.com/strongloop/loopback-boot/issues/4 as the `user` and `pass` properties that are part of the nodemailer transport object are not environment variables. 
extra space and a unrelated change, please revert