Temporary workaround for whatsapp issues.

Use the RFC-2732 specified hostname (for IPv6 literals) in places where it
makes sense to do so. We pass it to Socket factories / Authenticators and use
it in the request line as well.

bug: 26769689

(cherry picked from commit cdf3c4bc)

Change-Id: Icfdce464b4f6e4eeb9ec6161103aab3040b2adbb