Be able to set default object ACL on GCS upload

[asciimike]

Currently, there's no way to set the predefined object ACL on an object that is being uploaded (though there is in the REST API). One can overwrite the metadata with a new ACL, but that is a hard overwrite, and doesn't preserve existing ACLs, unlike add default ACL. It would be neat if we had an API that worked like:

var options = {
  predefinedAcl:'publicRead',
  validation: 'crc32',
  metadata: {/* add metadata here */}
};

bucket.upload('local/path/to/bar.txt', options, function(err, file) {
  // File is publicly readable!
});

[stephenplusplus]

Sounds like a good idea to me!

[stephenplusplus]

Sent a PR for this, feel free to test it out!

$ npm install --save stephenplusplus/gcloud-node#spp--1178