It proved to be dangerous to introduce conditional logic into recipes
and recipe modules to alternate between buildbot and luci modes, namely
it touches buildbot code paths, which can be very dangerous.

Instead, introduce "generic" default path config that configures
existing base paths from the built-in ones.

Also remove swarmbucket path config because it is not used.

R=iannucci@chromium.org
BUG=660481

Change-Id: Ide0e1f64913fe35766b997ab5b55f01f4c63aa58
Reviewed-on: https://chromium-review.googlesource.com/459234
Commit-Queue: Nodir Turakulov <nodir@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>