close over channels to avoid race
close over channels to avoid race

WARNING: DATA RACE
Write at 0x00c420198368 by goroutine 19:
  code.cloudfoundry.org/executor/depot/containerstore_test.glob..func2.10.10.1()
      /tmp/build/80754af9/diego-release/src/code.cloudfoundry.org/executor/depot/containerstore/containerstore_test.go:1589
Previous read at 0x00c420198368 by goroutine 43:
  code.cloudfoundry.org/executor/depot/containerstore_test.glob..func2.10.10.2.1()
      /tmp/build/80754af9/diego-release/src/code.cloudfoundry.org/executor/depot/containerstore/containerstore_test.go:1614

[#143253409]

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

cloudfoundry-incubator/executor