Add missing constraints to /info

Two of the default constraints, max_header_size and
max_meta_overall_size, don't get registered for the
/info response by the proxy server.

Rather than adding them individually to the proxy's
register_swift_info call, this patch proposes to
register all the constraints for /info at once
using the constraints.EFFECTIVE_CONSTRAINTS dict.
Any future additions to default constraints will
then be automatically included in /info.

Change-Id: I5c10d4c8eda90ba94745b6f89df85aafbb50f8ef
Merge "Add missing constraints to /info"