charm: avoid use of /bin/cp

Isolated tests should avoid use of external commands when possible.

Also update utils dependency so that we can use the new fs package
containing the Copy function.
provider/openstack: support zone placement
charm/testing: do not rely on copy overwriting
Merge pull request #37 from axw/provider-openstack-zone-placement

This is essentially the same as the work done for ec2 in https://github.com/juju/juju/pull/8. Like many other things in the two providers, there is a lot of overlap.

I have not yet updated dependencies.tsv; will do so when the goose branch lands (https://codereview.appspot.com/103900045).

A followup will add support for automatic spread across AZs.
Merge pull request #57 from rogpeppe/006-charm-no-cp

Isolated tests should avoid use of external commands when possible.

Also update utils dependency so that we can use the new fs package
containing the Copy function.
store: do not use environs/config

Also make charm.DirSuite use IsolationSuite.
Merge pull request #59 from rogpeppe/007-charm-no-envconfig

store: do not use environs/config

Also make charm.DirSuite use IsolationSuite.
Implemented ListNetworks in dummy provider and stubbed it out in the others
Merge pull request #58 from dimitern/511-environ-listnetworks-stubs

Introducing Environ.ListNetworks()

Provides a way for juju to discover what networks
are available from the provider. Later, we'll use
that information to discover networks initially
(at bootstrap) and to update them when they change.

Implemented in dummy provider only and stubbed it
out in the others

In a follow-up a concept of "pending networks" will
be introduced in state to hold such networks until
the user decides to use them (i.e. by running
juju add-network --existing).
Charm now validates YAML-loaded Actions schema

At the time the Actions schema is loaded from YAML, gojsonschema now
uses its Validate method to ensure that the loaded schema conforms to
JSON-Schema Draft 4.  The schema for JSON-Schema Draft 4 has been added
to the charm package for this purpose to avoid remote queries to the
spec.