checks if healthChecks is a key of app before checking length (#637)

[DeciderWill]

When grouping services with HAPROXY_DEPLOYMENT_GROUP without a health check marathon-lb crashes.

#637

[mesosphere-ci]

Can one of the admins verify this patch?

[mesosphere-ci]

Can one of the admins verify this patch?

[mesosphere-ci]

Can one of the admins verify this patch?

[mesosphere-ci]

Can one of the admins verify this patch?

[jkoelker]

ok to test

[jkoelker]

LGTM

[jkoelker]

test this please

[jkoelker]

Since for whatever reason CI integration is flaking, I ran it locally:

+ Build container image jkoelker/jkoelker-marathon-lb-dev:29b8b33c2574
+ Pushing image to hub
docker push jkoelker/jkoelker-marathon-lb-dev:29b8b33c2574
The push refers to repository [docker.io/jkoelker/jkoelker-marathon-lb-dev]
a08ce0dd8fa9: Pushed
0a399dd098ff: Pushed
7af717fb75ca: Pushed
4ad9376d6614: Pushed
f9fa827bbe35: Pushed
aa909696e36b: Mounted from library/debian
29b8b33c2574: digest: sha256:415340d129f2f5409854ce781973fc68c19755d893e6b2571d6a7348db7d5db5 size: 1580
+ Build devkit image mesosphere/marathon-lb-devkit:latest
+ Downloading 1.13.0.ee installer
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 1464M  100 1464M    0     0  22.7M      0  0:01:04  0:01:04 --:--:-- 35.9M
+ Starting DCOS enterprise cluster: marathon-lb-devkit
A cluster may take some time to be ready.
The amount of time it takes to start a cluster depends on a variety of factors.
If you are concerned that this is hanging, try "minidcos docker doctor" to diagnose common issues.
+ Discovering Cluster URL
+ Cluster URL: http://172.17.0.3
+ Discovering Public Node IP
+ Public Node IP: 172.17.0.5
+ Integration Testng with image jkoelker/jkoelker-marathon-lb-dev:29b8b33c2574
========================================= test session starts ==========================================
platform linux -- Python 3.7.3rc1, pytest-3.10.1, py-1.8.0, pluggy-0.11.0 -- /usr/bin/python3
cachedir: .pytest_cache
rootdir: /marathon-lb/ci, inifile:
plugins: timeout-1.3.3, dcos-test-utils-0.1
collected 20 items

test_marathon_lb_dcos_e2e.py::test_port[backends/docker_ippc.json] PASSED                        [  5%]
test_marathon_lb_dcos_e2e.py::test_response[backends/docker_ippc.json] PASSED                    [ 10%]
test_marathon_lb_dcos_e2e.py::test_port[backends/ucr_host.json] PASSED                           [ 15%]
test_marathon_lb_dcos_e2e.py::test_response[backends/ucr_host.json] PASSED                       [ 20%]
test_marathon_lb_dcos_e2e.py::test_port[backends/docker_bridge.json] PASSED                      [ 25%]
test_marathon_lb_dcos_e2e.py::test_response[backends/docker_bridge.json] PASSED                  [ 30%]
test_marathon_lb_dcos_e2e.py::test_port[backends/ucr_ippc.json] PASSED                           [ 35%]
test_marathon_lb_dcos_e2e.py::test_response[backends/ucr_ippc.json] PASSED                       [ 40%]
test_marathon_lb_dcos_e2e.py::test_port[backends/ucr_bridge.json] PASSED                         [ 45%]
test_marathon_lb_dcos_e2e.py::test_response[backends/ucr_bridge.json] PASSED                     [ 50%]
test_marathon_lb_dcos_e2e.py::test_port[backends/docker_host.json] PASSED                        [ 55%]
test_marathon_lb_dcos_e2e.py::test_response[backends/docker_host.json] PASSED                    [ 60%]
test_marathon_lb_dcos_e2e.py::test_port[backends_1.9/docker_ippc.json] SKIPPED                   [ 65%]
test_marathon_lb_dcos_e2e.py::test_response[backends_1.9/docker_ippc.json] SKIPPED               [ 70%]
test_marathon_lb_dcos_e2e.py::test_port[backends_1.9/ucr_host.json] SKIPPED                      [ 75%]
test_marathon_lb_dcos_e2e.py::test_response[backends_1.9/ucr_host.json] SKIPPED                  [ 80%]
test_marathon_lb_dcos_e2e.py::test_port[backends_1.9/docker_bridge.json] SKIPPED                 [ 85%]
test_marathon_lb_dcos_e2e.py::test_response[backends_1.9/docker_bridge.json] SKIPPED             [ 90%]
test_marathon_lb_dcos_e2e.py::test_port[backends_1.9/docker_host.json] SKIPPED                   [ 95%]
test_marathon_lb_dcos_e2e.py::test_response[backends_1.9/docker_host.json] SKIPPED               [100%]

================================ 12 passed, 8 skipped in 197.43 seconds ================================