bump bbs
bump bbs

[finishes #149906903]

Submodule src/code.cloudfoundry.org/bbs 822e5be6..31d35bef:
  > Add preloaded+layer rootfs provider type to cell presences

Signed-off-by: Danny Cao <5ffc8b7cff3b9f2acb630fd157ff837ced3278ae@us.ibm.com>

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