bump benchmarkbbs
bump benchmarkbbs

Submodule src/code.cloudfoundry.org/benchmarkbbs 8bfd668f..188b3d4e:
  > Use custom locket client

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