Always propagate some environment variables to RBE

Always propagate LANG, LC_MESSAGES and PYTHONDONTWRITEBYTECODE
to RBE to get more consistent behavior between local actions and
RBE.

Bug: 182415460
Bug: 190593001
Test: treehugger
Change-Id: I726e6f02fd3ef77e158baf6fde77ffb7247a1375
Merged-In: I726e6f02fd3ef77e158baf6fde77ffb7247a1375