Add support for session tickets

This change adds a session ticket cache to DnsTlsTransport,
which should reduce the startup time for new sockets by 1 RTT.
This change is complex because queries may be issued on any
thread, all threads must share the cache, and we need some way
of expiring old entries from the cache.

Test: Integration tests pass.  Wireshark shows tickets in use.
Bug: 63447621
Change-Id: I756119a9d82bcba0b309a2dd84414e2fb3d4956f
7 files changed