state: prevent `using unknown collection "remoteApplications"` error

[babbageclunk]

Description of change

The state/applicationByName function would always try to get a remote application, and if that wasn't found would get an application instead. Change this to try returning a local application first (this will generally be the right thing), then if that's not found and the cross model flag is set try getting a remote application instead.

If neither are found, we still return the error application "needle" not found. This is less confusing for the user, since it's probably what they were intending, and remote applications are also (conceptually) applications so it's not wrong in that case either.

QA steps

• Bootstrap a controller with the crossmodel flag disabled.
• Deploy some applications and relate them.
• Check that the log contains no messages containing unknown collection "remoteApplications"

[babbageclunk]

$$merge$$

[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/10904

[babbageclunk]

Gah, test run killed because we exceeded our instance quota.

$$merge$$

[jujubot]

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