The Google GFE replies to HEAD requests with the END_STREAM bit in an
empty DATA frame, not in the response HEADERS. The Go Transport code
mistook this to mean the Content-Length was real.

Worked around in:
https://github.com/GoogleCloudPlatform/gcloud-golang/commit/645322e7db5d89c44d1f3925028479ac7dbc8680

Reported internally in b/27820181.

Change-Id: Id31a047e2277d7d90560fca264919e239ec76d74
Reviewed-on: https://go-review.googlesource.com/21061Reviewed-by: Dave Day <djd@golang.org>