CBLT-272: use --fail flag on curl for cbfs upload commands, so that the build fails if the package is not retained.

Change-Id: I52ec28207c4e5ed6aa9ff1f52652f106fd9e4802
Reviewed-on: http://review.couchbase.org/36328
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>