Code review comment for lp://qastaging/~bac/juju-quickstart/packaging-tweaks

*** Submitted:

Update HACKING doc.

Reference the two different packaging recipes for trusty and beyond and
for
the pre-trusty series.

The packaging branches are now two separate series:
lp:juju-quickstart/packaging and
lp:juju-quickstart/packaging-pre-trusty.
Referencing them in the recipes is cleaner than using bare branch names.

Also add a QA step for environments.yaml generation.

R=frankban
CC=
https://codereview.appspot.com/103310043

https://codereview.appspot.com/103310043/