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

[delivers #129111477]

Submodule src/code.cloudfoundry.org/diego-stress-tests f59ec21..212c1eb:
  > remove unreachable code
  > increase timeout from 0.5*interval to 0.9*interval

Signed-off-by: Joachim Valdez <f4115f6bcd6858c277581a1d9da83b9914dce2c3@us.ibm.com>

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