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: I7d884baad621eaa22cdef4f4b980044616116513
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: I46e1b43df3a5e59018f604ce1ae20bd62744a45b