On Xenial: install /usr/bin/env: 'python': No such file or directory

[Ryan Beisner]

odl-controller needs pre-install hook treatment for python 2.

2016-03-10 01:51:23 DEBUG juju.worker.uniter modes.go:31 [AGENT-STATUS] executing: running install hook
2016-03-10 01:51:23 INFO install /usr/bin/env: 'python': No such file or directory
2016-03-10 01:51:23 INFO juju.worker.uniter.context context.go:579 handling reboot
2016-03-10 01:51:23 ERROR juju.worker.uniter.operation runhook.go:107 hook "install" failed: exit status 127
2016-03-10 01:51:23 DEBUG juju.worker.uniter modes.go:31 [AGENT-STATUS] failed: run install hook
2016-03-10 01:51:23 INFO juju.worker.uniter modes.go:569 ModeContinue exiting
2016-03-10 01:51:23 INFO juju.worker.uniter modes.go:567 ModeHookError starting
2016-03-10 01:51:23 DEBUG juju.worker.uniter.filter filter.go:601 want resolved event
2016-03-10 01:51:23 DEBUG juju.worker.uniter.filter filter.go:595 want forced upgrade true
2016-03-10 01:51:23 DEBUG juju.worker.uniter.filter filter.go:731 no new charm event
2016-03-10 01:51:23 DEBUG juju.worker.uniter modes.go:31 [AGENT-STATUS] error: hook failed: "install"

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/291139
Committed: https://git.openstack.org/cgit/openstack/charm-odl-controller/commit/?id=a1cf699ee9083c8e713ded398340590c194b1ea1
Submitter: Jenkins
Branch: master

commit a1cf699ee9083c8e713ded398340590c194b1ea1
Author: James Page <email address hidden>
Date: Thu Mar 10 12:23:01 2016 +0000

    Add support for Ubuntu Xenial

    Xenial does not install python2 by default; ensure that python2
    and minimal module dependencies are installed prior to trying
    to execute any python2 based hooks.

    Update amulet tests to drop shared-db relation for n-gateway.

    This change also includes a resync of charm-helpers to pickup
    new changes for systemd support.

    Change-Id: Icef9679cd1d1c96e8aa87bcedcf9735a41af8d52
    Closes-Bug: #1555422