Support HTTP responses with no body

Successful upsertLocalAuthInfo cloud requests returns no body and no
content type.

BUG=25766813

Change-Id: Id4deb57c8dfea04196f77c80b6f40ce62db9fa6f
Reviewed-on: https://weave-review.googlesource.com/1799
Reviewed-by: Alex Vakulenko <avakulenko@google.com>
4 files changed