linux wrapper: adding LED device simulator and commands:
_ledflasher._set
_ledflasher._toggle
Change-Id: I45a01769e827fc8dec3f0f37bb50111f9b77aaf4
Reviewed-on: https://weave-review.googlesource.com/1226
Reviewed-by: Vitaly Buka <vitalybuka@google.com>