Add EarlyChangeCipherSpec tests.

Adapted from patch in https://www.imperialviolet.org/2014/06/05/earlyccs.html.

Change-Id: I14bf314d105780e23e6bd09217870deff5744979
Reviewed-on: https://boringssl-review.googlesource.com/1292
Reviewed-by: Adam Langley <agl@google.com>