Add bootstrap image to upgrade tarball

In order to make possible update bootstrap image on Fuel node, we need
to ship it within our tarball.

Implements blueprint upgrade-to-5-0-1

Partial-Bug: #1336689

Change-Id: I45e9643e999f9b748703b6358519980298d5abc3
Merge "Add bootstrap image to upgrade tarball" into stable/5.0