Implement AES-GCM in tlslite.

This adds controls to the C++ test server but doesn't use them yet. Also
ensure that tlslite never selects a 1.2 cipher suite when negotiating an
older version.

BUG=450733

Review URL: https://codereview.chromium.org/875683002

Cr-Commit-Position: refs/heads/master@{#313809}
17 files changed