all: use local testing charm repository
Merge pull request #1048 from rogpeppe/018-local-charm-repo

all: use local testing charm repository

This change is large, but almost entirely mechanical.
The only new code is the single line in the testcharms package.
All the charms have been copied without alteration from
the charm.v4 repo - at a later stage this should be pruned
down to just the charms required by the juju tests (and
possibly split up too).