This patch adds standard SSL options to IPA config and makes use of them
when making HTTP requests.
For now, a single set of certificates is used when needed.
In the future configuration can be expanded to allow per-service
certificates.
Besides, the 'insecure' option (defaults to False) can be overridden
through kernel command line parameter 'ipa-insecure'.
This will allow running IPA in CI-like environments with self-signed SSL
certificates.
Change-Id: I259d9b3caa9ba1dc3d7382f375b8e086a5348d80
Closes-Bug: #1642515
fdd11b54a5