cmd/cmdtesting: rename from cmd/testing

[rogpeppe]

Also move the command testing helpers from
the top level testing package.

This is because we don't want to add a cmd/modelcmd
dependency to juju/testing, but having cmd testing
helpers in one place seems like a Good Thing.

Left for the future: use the almost-identical github.com/juju/cmd/cmdtesting
throughout.

We rename the RunCommand that was currently in cmd/testing
to RunCommandWithDummyProvider to avoid the name clash.

We also needed to make the resource/cmd tests external because of
a dubious-looking import cycle caused by this import cycle:

package github.com/juju/juju/resource/cmd (test)
imports github.com/juju/juju/cmd/cmdtesting
imports github.com/juju/juju/provider/dummy
imports github.com/juju/juju/apiserver
imports github.com/juju/juju/resource/resourceadapters
imports github.com/juju/juju/resource/cmd

The apiserver package should really not import any cmd packages,
but that can be fixed some other day.

QA: no regressions.

[mhilton]

LGTM

[mhilton]

!!build!!

[rogpeppe]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju

[jujubot]

Build failed: Tests failed
build url: http://juju-ci.vapour.ws:8080/job/github-merge-juju/10638

[rogpeppe]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju

[jujubot]

Build failed: Tests failed
build url: http://juju-ci.vapour.ws:8080/job/github-merge-juju/10639

[rogpeppe]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju