The charm-helpers project have re-licensed to Apache 2.0
inline with the agreed licensing approach to intefaces,
layers and charms generally.
Resync helpers to bring charmhelpers inline with charm
codebase.
Change-Id: I99e94eec42adc19ab92b14a20e59cc60360e0b58
Add charmhelpers.contrib.hardening and calls to install,
config-changed, upgrade-charm and update-status hooks.
Also add new config option to allow one or more hardening
modules to be applied at runtime.
Change-Id: If0d1e10b58ed506e0aca659f30120b8d5c96c04f