bump diego-stress-tests
bump diego-stress-tests

[delivers #129111477]

Submodule src/code.cloudfoundry.org/diego-stress-tests 212c1eb..1e3d5b2:
  > close the response.body so we won't leak connections

Signed-off-by: Andrew Edgar <cc1cbeb507c6357651b55d7c7887132c42e42341@ca.ibm.com>

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