Show user-friendly error for invalid HTTP certificates

Show user-friendly error for invalid HTTP certificates

Makes the openstack client backend detect SSL certificate validation
failures and propogate them as nicer errors that users have a chance
of comprehending.

The hint to set ssl-hostname-validation to off is a judgement call,
but is common for tools like curl and wget when they reject a cert.

Ideally the hostname and perhaps other details would also be included
in the message, but this should do for now.

https://code.launchpad.net/~gz/juju/os_https_pretty_error/+merge/121273

Requires: https://code.launchpad.net/~gz/juju/os_https_certs_1026102/+merge/118602

(do not edit description out of merge proposal)

[gz, 2012-08-24 19:38:57]

Please take a look.

[jimbaker, 2012-08-25 22:54:43]

+1, looks good to me. I think one test could be made more readable using
inlineCallbacks, but that's a real minor.

https://codereview.appspot.com/6480062/diff/1/juju/providers/openstack/tests/...
File juju/providers/openstack/tests/test_client.py (right):

https://codereview.appspot.com/6480062/diff/1/juju/providers/openstack/tests/...
juju/providers/openstack/tests/test_client.py:156: 
This test can use @inlineCallbacks and be a bit simpler too; simply change the
last line to

yield self.assertFailure(osc.authenticate(), errors.ProviderInteractionError)
self.assertIn("Bad HTTPS certificate", str(error))

[gz, 2012-08-28 12:35:19]

Had missed there was an exception type in juju.errors for doing this anyway,
switched the code to use that. As the exception was confused about what its
param was, also sorted that out.

On 2012/08/25 22:54:43, jimbaker wrote:
> +1, looks good to me. I think one test could be made more readable using
> inlineCallbacks, but that's a real minor.

Now it's using a custom exception type, I just remove the str checking which is
covered in juju.tests.test_error anyway.