Sync charm-helpers from lp:charm-helpers
[gnuoy, r=tribaal] Sync charm helpers from lp:~openstack-charmers/charm-helpers/stable
Resync charmhelpers for cache bug fixes
[gnuoy,r=tribaal] Resync charmhelpers for apt cache bug fixes
Cherry pick fix from next branch for ambiguous nrpe-external-master relations.
[james-page,r=gnuoy] Cherry pick fix from next branch for ambiguous nrpe-external-master relations.
Rebase on trusty branch to remove divergence
[trivial] sort out typo in config.yaml