If -m option value starts with "luci.", most probably the user intends
to schedule a build on a LUCI bucket. Print an error message asking
the user to use -B option.

Bug: 749696
Change-Id: If7a038a1f629ee808e3261ae1c753e388bfea893
Reviewed-on: https://chromium-review.googlesource.com/707534Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Nodir Turakulov <nodir@chromium.org>