Create a test task to verify muster-gather log collection

Create a test task to verify muster-gather log collection

muster-gather should collect log without an error with the following command:
$ $ oc adm must-gather --image=registry.redhat.io/openshift-service-mesh/istio-must-gather-rhel7

We need a test case to automate this check in the 2.0.1 release.