Adds ability to override mount with publicServerURL for production uses

[flovilmart]

superseds #1270
fixes #1131

also adds a sanity so we don't keep trailing / in mount or publicServerURL

[codecov-io]

Current coverage is 93.02%

Merging #1287 into master will not affect coverage as of a929dde

@@            master   #1287   diff @@
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  Stmts         5275    5289    +14
  Branches       960     965     +5
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+ Hit           4907    4920    +13
  Partial         11      11       
- Missed         357     358     +1

Review entire Coverage Diff as of a929dde

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[drew-gross]

I think we actually don't want to do this, since we don't really want internal queries to go back out to the public internet to do dns resolution and so on.

[flovilmart]

We only use .mount to give back to the clients (and in file adapters)

[flovilmart]

RestWrite.prototype.location = function() {
  var middle = (this.className === '_User' ? '/users/' :
                '/classes/' + this.className + '/');
  return this.config.mount + middle + this.data.objectId;
};

It's the only occurrence besides GridStoreAdapter and all FilesAdapter which both need public URL's otherwise create files that are referenced by the requested host i.e.: localhost:1337

And RestWrite.prototype.location is only used to fill the responses of object creation and OAuth login, never internally AFAIK.

Do you see other cases?

[drew-gross]

Ah right this is only for the mount point, not the URL. In that case this looks good.

[flovilmart]

This is the full URL that is returned to the clients, mount is currently inferred :

function handleParseHeaders(req, res, next) {
  var mountPathLength = req.originalUrl.length - req.url.length;
  var mountPath = req.originalUrl.slice(0, mountPathLength);
  var mount = req.protocol + '://' + req.get('host') + mountPath;
...