Remove superfluous requirement for principal units only
go fmt
KVM containers can now be created using a user-provided SimpleStreams URL as a base.
MachineConfig now contains field for which SimpleStream to utilize.
added a periodic worker which will call a function periodically based on an input duration
review feedback. Don't use time.Tick and improve the tests
split new and run functions, add tests for calls to Stop
improved the kill test
implemented ErrKilled for signaling that the call was asked to stop
Merge pull request #469 from mattyw/add-periodic-worker

added a periodic worker

The periodic worker will call a function periodically based on an input duration
Merge pull request #398 from katco-/lp-1322302-local-slow-transition

KVM containers can now be created using a user-provided SimpleStreams URL as a base.

First step to alleviating https://bugs.launchpad.net/juju-core/+bug/1322302. Second PR to follow which will make apt-get behavior more configurable.
Merge pull request #447 from marcoceppi/run-dmc-and-subordinates

Remove superfluous requirement for juju run against only principal units

Currently, with `juju run`, only principal units are allowed to receive run requests, barring subordinates from the list of allowed units which can have commands executed against with `juju run`. This change removes that requirement allowing just units that have an assigned machine to receive run events.

Error that was occurring previously:

```
marco@home:~$ juju run --unit subordinate/0 "config-get debug"
ERROR subordinate/0 is not a principal unit.
```

This change aims to correct this behavior. After compiling and bootstrapping the following results when running `juju run` against a subordinate:

```
marco@home:~/go/bin$ ./juju run --unit subordinate/0 "config-get"
debug: false
```

As far as I can tell, from my testing, this has not created any regressions and addresses the above stated issue of not being able to use `juju run` against subordinates in an environment.
Merge branch 'master' of https://github.com/juju/juju