Adding configuration for the ability to delete a build slave when it is
released, for cloud-based VM pools

Change-Id: I89ec3b229abe7095788fd13d4238eedf1ef22ef3
Reviewed-on: https://q.tasktop.com/alm/s/c2c-oss/gerrit/132
Reviewed-by: Myles Feichtinger <myles.feichtinger@tasktop.com>
Reviewed-by: Michael Nelson <michael.nelson@tasktop.com>
Tested-by: Michael Nelson <michael.nelson@tasktop.com>