CBD-1425:  use "fetch-manifest.rb" instead of "repo init"

Change-Id: Ifa4083c02a02b1fb71e6282f902b7d8fbf20504e
Reviewed-on: http://review.couchbase.org/40430
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>