Abstract charm relations into a separate thread

juju doesn't provide a way to pre-emptively set services that will be
related whether the related charm exists or not. This creates a thread
that just goes through a list of charms to be related and will run
until those relations complete.

Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>
Pulling latest command output changes into this feature branch
Better error handling for charms not ready to relate

Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>
rename variable to be a little more obvious on its intentions

Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>
Merge pull request #56 from battlemidget/feature-charm-queue-1

Abstract charm relations into a separate thread