Secure Key Management

Secure Key Management

This patchset implements the Secure Key Management feature
as described in Gerrit 1429, enabling support for native charms
deployed to machines provisioned by the Resource Orchestrator.

- Implement GetPublicKey, which will provide the public key to be
injected into new machines
- Support machine placement, to provision an existing machine for use
with juju
- Automatically create a SSH keypair to be used for provisioning
- Add method to check if a charm is deployed (CI)
- Update integration tests to use new ssh key workflow

Signed-off-by: Adam Israel <adam.israel@canonical.com>