Support diffing a local ksonnet app to the live application state (resolves #239)

[jessesuen]

Example output:

$ argocd app diff argocd-cdp --local . --env cdp
===== ServiceAccount application-controller ======
===== Deployment application-controller ======
===== Role application-controller-role ======
===== RoleBinding application-controller-role-binding ======
===== ServiceAccount argocd-server ======
===== Role argocd-server-role ======
===== RoleBinding argocd-server-role-binding ======
===== Secret argocd-secret ======
 {
   "apiVersion": "v1",
   "kind": "Secret",
   "metadata": {
     "annotations": {
       "com.intuit.idps/policy-id": "p-tvzl0flgkgp9",
       "com.intuit.idps/secrets": "prod-https-crt=server.crt;prod-https-key=server.key"
     },
     "labels": {
       "applications.argoproj.io/app-name": "argocd-cdp",
-      "com.intuit.idps/appliance": "argocd-production-56erqf.pd.idps.a.intuit.comm"
+      "com.intuit.idps/appliance": "argocd-production-56erqf.pd.idps.a.intuit.com"
     },
     "name": "argocd-secret"
   },
   "type": "Opaque"
 }

===== Deployment argocd-server ======
===== Service argocd-server ======
===== ConfigMap argocd-cm ======
===== ConfigMap argocd-rbac-cm ======
===== Deployment argocd-repo-server ======
===== Service argocd-repo-server ======