Code review comment for lp:~hazmat/pyjuju/hooks-with-formula-dir

This looks good, thanks!

Two details to ponder about before merging:

[2]

The variable name: should it be prefixed by ENSEMBLE_ like the rest of them? Is it more common to have _PATH rather than _DIR?

[3]

Would be good to document the directory next to the hooks description in the formulas spec.