This allows the cipd client to process refs with slashes in them.

Also it is compiled with cgo on OSX, which should help with DNS
resolution errors that happen on some machines.

R=vadimsh@chromium.org

Bug: 811974, 803673
Change-Id: If298db5cfe0e10e3734deb4215bf82b95ff5e09e
Reviewed-on: https://chromium-review.googlesource.com/940521
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>