Add POST and DELETE to tempurl default methods

The tempurl middleware supports any configured HTTP methods, but the
default set was only GET, PUT, and HEAD, so cluster operators had to
take action to enable POST and DELETE. This commit changes the
defaults to include POST and DELETE.

Note that this doesn't affect any existing temporary URLs at all; the
method is baked into the signature (temp_url_sig query param), so no
new access is granted to a holder of a temporary URL by this
change. It simply gives more flexibility to creators of temporary
URLs.

Change-Id: I5bc15bbd2968ab7bedcd7c0df10f2ec825537191
Merge "Add POST and DELETE to tempurl default methods"