* <ul>
 * <li>os.name: The operating system name</li>
 * <li>os.arch: The operating system architecture</li>
 * <li>os.version: The operating system version</li>
 * </ul>
 * <p>
 * Supported OS families include:
 * <ul>
 * <li>windows: All Windows variants</li>
 * <li>win9x: Windows 95, 98, ME, CE</li>
 * <li>winnt: Windows NT variants</li>
 * <li>unix: Unix-like systems (including Linux)</li>

With fast fallback, OkHttp attempts to connect to multiple web servers concurrently. It keeps whichever route connects first and cancels all of the others. Its rules are:

 * Prefer to alternate IP addresses from different address families, (IPv6 / IPv4), starting with IPv6.
 * Don't start a new attempt until 250 ms after the most recent attempt was started.
 * Keep whichever TCP connection succeeds first and cancel all the others.