GetUnitTests() has named params {run_on_python2, run_on_python3}.
This CL adds these params to GetUnitTestsRecursively() so they can be
forwarded to GetUnitTests().

Bug: https://crbug.com/1054018
Change-Id: I06ac25a37f94cdea1cdc91954b70113e54cfdd15
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2107610Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Samuel Huang <huangs@chromium.org>