Move SendV2ClientHello to handshake coverage tests.

It's a different handshake flow with more state machine coverage. We should
make sure to test the asynchronous version.

Change-Id: I0bb79ca7e6a86bd3cac66bac1f795a885d474909
Reviewed-on: https://boringssl-review.googlesource.com/1454
Reviewed-by: Adam Langley <agl@google.com>