Get each charm up to date with lp:charm-helpers for release testing.

Change-Id: I1ac07a964adadc53e1ae1359ffb3d59171fb72d0

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: Icedfb79814e186290a3120d953c9077e4e4504fe