bump bbs
bump bbs

Submodule src/code.cloudfoundry.org/bbs f8107a3f..8340e78a:
  > Tiny simplification in desired_lrp_handlers
  > Fix misleading test in migration manager

Signed-off-by: Stephane Jolicoeur <cd2742f5f5d6c8654adbc4b36f13fda4256e0aed@pivotal.io>

cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release