bump atc
bump atc

[finishes #114448277]

Submodule src/github.com/concourse/atc 02d903a..c12191d:
  > reset build preparations when pipeline stopped
  > reset the build prep when the build is scheduling

Signed-off-by: Anand Gaitonde <4f0ff06b2390eeadb0769d298cbdb3dc6df4c73d@pivotal.io>
Signed-off-by: Chris Brown <eb0819782e2e967e3d4f4d71eab0c647ed2659cf@pivotal.io>

concourse/concourse,cjcjameson/concourse,concourse/concourse,cjcjameson/concourse,concourse/concourse,concourse/concourse,cjcjameson/concourse,concourse/concourse