Test SHA-256 and SHA-384 CBC-mode cipher suites.

These were added in TLS 1.2. They are like the standard AES-CBC cipher suites,
but use different HMACs.

Change-Id: Ib89ddebd1aa398b1347f8285f5d827068b1bd181
Reviewed-on: https://boringssl-review.googlesource.com/1730
Reviewed-by: Adam Langley <agl@google.com>