Because of the way go handles flags, passing a flag that is not defined
will cause an error. In our case, if we kept this as a flag, then
third-party shims would break when they see this new flag. To fix this,
I moved this new configuration option to an env var. We should use env
vars from here on out to avoid breaking shim compat.
Signed-off-by: Michael Crosby <crosbymichael@gmail.com>