scripts: install-rkt.sh: fail install-pak on errors
scripts: install-rkt.sh: fail install-pak on errors

When install-pak (called from install-rkt.sh) fails at some point
abort packaging.

This is based on a discussion in
https://github.com/coreos/rkt/pull/3127#discussion-diff-76763179 where
it was agreed upon that aborting on unexpected failures would be
desirable.

Wilybald/rkt,Wilybald/rkt,Wilybald/rkt,Wilybald/rkt