HostingServiceHTTPRequest.open() built a

CertificateVerificationHTTPSHandler without telling it which server the

request was for. The handler's hostname and port arguments therefore had

no callers, and the handler was left without an SSL context until

https_open() built one from the request URL.
These are now passed in from the request's URL, so the context is available

as soon as the handler is constructed.

BuildSSLContextFromSSLCertTests.test_open_with_https failed before this

  change, asserting against a None context. It now passes.
Ran unit tests for reviewboard.certs and reviewboard.hostingsvcs.