[3.1] Bootstrap build failing on building reference packages

[adaggarwal]

The current 3.1 build is failing on bootstrapping due to DownloadFile task for the tarball(in source-build-reference-packages build). This results on network dependence. Because we turn it off in bootstrap build, the step is currently failing.

[dseefeld]

This appears to be fixed now. The bootstrap build is succeeding in the 3.1 branch.