run-as-hook bails, ignores default env in environment.yaml, returns JUJU_ENV_UUID

[Peter Petrakis]

= Summary=
some better error return messages are required, if the env
isn't specified the returned error is ambiguous. What confused me
was my default env was defined in the YAML and seemingly ignored.

= Reproduction=

$ jitsu --version
jitsu 0.22

$ jitsu run-as-hook collectd-server/1 config-get graph-port
'JUJU_ENV_UUID'

That var is defined on the instance and uniform through the environment

also,

$ echo JUJU_ENV
JUJU_ENV

Once that is set, it works, or I pass it via -e

I can also work around it by leaving the env unset and grabbing
JUJU_ENV_UUID from the instances

$ juju ssh collectd-server/1 grep -R JUJU_ENV_UUID /etc 2>/dev/null
/etc/init/juju-collectd-server-1.conf:env JUJU_ENV_UUID="39ff9d9f960c446f9bfd0a8ed68ccd7d"

$ export JUJU_ENV_UUID="39ff9d9f960c446f9bfd0a8ed68ccd7d"

$ jitsu run-as-hook collectd-server/1 config-get graph-port
80