Rename testExecutorEnvs --> executorEnvs.

This was changed, but in fact, it's used for things other than tests.
So I've changed it back.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #747 from pwendell/executor-env and squashes the following commits:

36a60a5 [Patrick Wendell] Rename testExecutorEnvs --> executorEnvs.
(cherry picked from commit 3ce526b168050c572a1feee8e0121e1426f7d9ee)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>