upgrade-juju: don't auto-upload with --version

[axw]

If you pass --version to upgrade-juju, Juju should
not attempt to automatically build and upload the
agent; it should always get the specified version
from streams.

Fixes https://bugs.launchpad.net/juju/+bug/1626784

QA

1. bootstrap 2.0rc1:

   juju bootstrap lxd lxd --config agent-metadata-url=http://juju-dist.s3.amazonaws.com/parallel-testing/agents --config agent-stream=revision-build-4415

2. Confirmed that the agent is 2.0rc1.1, because there's no metadata for 2.0rc1.

3. Confirmed that the stream has 2.0rc2 agents, using github.com/axw/juju-tools.

4. with "2.0rc2" (master), ran upgrade-juju:

   juju upgrade-juju -m controller --version 2.0-rc2

Confirmed the resultant version is 2.0rc2, not 2.0rc2.1.

[perrito666]

LGTM

[mjs]

Looks good although I wonder if the help text should be updated to mention that local tools will never be used if --version is used?

[axw]

Looks good although I wonder if the help text should be updated to mention that local tools will never be used if --version is used?

The help docs don't mention the auto-upload functionality. You can still use --version with --build-agent, though I'm not sure why you would.

[axw]

$$merge$$

[jujubot]

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