This helps with creating a separate binary to perform split
handshakes, in that the test state must be communicated to, and
retrieved from, the handshaker binary using a socket.

Change-Id: I9d70a9bb3d97dd339aab4f51c6de75f71e4fe72d
Reviewed-on: https://boringssl-review.googlesource.com/29704
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

This makes |TestState| and |TestConfig| accessible outside
bssl_shim.cc, as well as the functions SetupCtx() and NewSSL(), which
become methods on |TestConfig|.  A whole mess of callbacks move in
order to support this change.

Along the way, some bits of global state are moved (e.g. the global
test clock) and made self-initializing.

This helps with creating a separate binary to perform split
handshakes.

Change-Id: I39b00a1819074882353f5f04ed01312916f3cccb
Reviewed-on: https://boringssl-review.googlesource.com/29345
Commit-Queue: Matt Braithwaite <mab@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: David Benjamin <davidben@google.com>