Try JUJU_CHARM_*_PROXY settings when fetching jenkins deb

[dannf]

If our model has juju proxy settings and we've been told to
fetch a specific deb, set the corresponding *_proxy variables
when doing so. If the user has set JUJU HTTP(S)/FTP proxies,
but has pointed us to an internally hosted deb, hopefully
they've also set JUJU_CHARM_NO_PROXY appropriately. But,
just in case, leave the fallback of fetching w an unmodified
environment.

[freeekanayaka]

There are failing tests, I also have a small nit.

[dannf]

Oh - but still failing tests. I'll look into that.

[dannf]

I fixed one of the coverage tests. For the other, I need to mock a non-zero wget exit code, but I'm not sure how to do that. @freeekanayaka - do you have any advice there?

[freeekanayaka]

@dannf looking

[freeekanayaka]

@dannf to be able to write a test we'd need to teach the fake wget to use a different URL if it finds an "http_proxy" variable in the environment (the environment should be available in the proc_args dict that the Wget.call method receive).

Then you could write a test like:

    def test_install_jenkins_remote(self):
        """
        If the 'release' config is set to a remote URL, and the JUJU_CHARM proxy environment
        variables are set, then the charm first tries to download the deb using the proxy and falls
        back to no proxy in case of failures.
        """
        self.useFixture(EnvironmentVariable("JUJU_CHARM_HTTP_PROXY", "1.2.3.4"))
        self.fakes.processes.wget.locations[
            "http://jenkins-1.2.3.deb"] = b"data"
        orig_release = hookenv.config()["release"]
        try:
            hookenv.config()["release"] = "http://jenkins-1.2.3.deb"
            self.packages.install_jenkins()
            self.assertEqual(
                ["install"], self.fakes.processes.dpkg.actions["jenkins"])
        finally:
            hookenv.config()["release"] = orig_release

which would hit the new code path that you added in this branch.

It should be relatively easy to modify Wget, but for now I think we can just add a "no cover" directive for this new code, e.g.:

except subprocess.CalledProcessError: # pragma: no cover
            if len(proxy_env) == 0:
                raise
            subprocess.check_call(("wget", "-q", "-O", target, url))

I can file a bug against systemfixtures to track this.