Support invoking helm test in errand

[gberche-orange]

As a developer, in order to save time on manual tests, I need the bosh release to invoke helm test when installing a chart

Example output on existing charts

$ HELMS=$(helm list | awk '{print $1}' | grep -v NAME)
$ for h in $HELMS ; do helm test $h; done;
    No Tests Found
    No Tests Found
    RUNNING: elasticsearch-eocgf-test
    PASSED: elasticsearch-eocgf-test
    No Tests Found
    No Tests Found
    RUNNING: gitlab-unicorn-test-runner-un8jd
    FAILED: gitlab-unicorn-test-runner-un8jd, run `kubectl logs gitlab-unicorn-test-runner-un8jd --namespace gitlab` for more info
    Error: 1 test(s) failed
    No Tests Found
    No Tests Found
    No Tests Found
    RUNNING: kubeapps-chartsvc-test
    PASSED: kubeapps-chartsvc-test
    RUNNING: kubeapps-dashboard-test
    PASSED: kubeapps-dashboard-test
    RUNNING: kubeapps-tiller-proxy-test
    PASSED: kubeapps-tiller-proxy-test
    No Tests Found
    No Tests Found
    No Tests Found
    No Tests Found
    No Tests Found
    RUNNING: traefik-test
    PASSED: traefik-test
    No Tests Found
    No Tests Found

[gberche-orange]

Alternatives:

• helm install action should offer granular / faithfull flags wrt to helm cli #24 https://github.com/orange-cloudfoundry/helm-kubectl-boshrelease#add-helm-chart will now support a new field cmd to replace default update with a new command such as lint or test
• a new errand job in helm-kubectl-boshreleaserelease to provide dedicated errands to smoke tests to ease ops experience