Update rethinkdb to v8 API version 3.21

Signed-off-by: Anatol Pomozov <anatol.pomozov@gmail.com>
New v8
comments
Do not make dependencies for v8
Merge branch 'atnnn/newv8' into HEAD

Review 1192 by @tryneus
Use python2 to build v8
Merge branch 'next' into sam_alt