Amphtml: *_HOST URL substitutions use hostname, omit port number

[src-code]

Currently (at least as of v1457112743399) the SOURCE_HOST, CANONICAL_HOST and AMPDOC_HOST URL substitutions rely on the hostname property of the anchor element, not host. Because of this, the port number is omitted. This can cause problems when referencing hosts serving on non-standard ports, for example in pre-production environments.

I'd like to propose that these *_HOST vars should be changed to rely on host, and that new variables be introduced for *_HOSTNAME that would preserve the existing behavior. This would of course be a breaking change, but would be more consistent going forward. (And really, the impact may be minimal, so perhaps calling it a breaking change is being overly cautious?)

[dvoytenko]

I have no problem with this. @cramforce what do you think?

[rudygalfi]

Maybe combined with vendors.js updates we can do this?

[dvoytenko]

I think we should just go ahead and do it. /to @mkhatib

[rudygalfi]

@mkhatib when you start on this, please update the milestone. Thanks!

[mkhatib]

This sounds good. This hopefully won't break anyone's current usage as I'd imagine people don't use ports in their prod-setup.