Building the image using dib no longer ignores the base element

When we build our image using dib, we should no longer use the -n flag which
suppresses the base element. With this fix, our first-boot.d script is now
being run on boot and the guest agent is installed successfully.

Fixes bug: 1182269

Change-Id: Ibdeb1f19b7b3e19e5709051251cdba1a99eda588