Added file based secrets support (#404)

* Added file based secrets support

(cherry picked from commit f1d4bbb)

* Fixed service account credential source

(cherry picked from commit c6946cc)

* Fix file based secrets

(cherry picked from commit edbcc70)

frameworks/kafka/universe/marathon.json.mustache

@@ -15,6 +15,15 @@
     "DCOS_SERVICE_SCHEME": "http"
   },
   {{#service.service_account_secret}}
+  "container": {
+    "type": "MESOS",
+    "volumes": [
+      {
+        "containerPath": "secrets/service-account.json",
+        "secret": "serviceCredential"
+      }
+    ]
+  },
   "secrets": {
     "serviceCredential": {
       "source": "{{service.service_account_secret}}"
@@ -68,8 +77,8 @@
     "BROKER_PORT": "{{brokers.port}}",
 
     {{#service.service_account_secret}}
-    "DCOS_SERVICE_ACCOUNT_CREDENTIAL": { "secret": "serviceCredential" },
-    "MESOS_MODULES": "{\"libraries\":[{\"file\":\"libmesos-bundle\/lib\/mesos\/libdcos_security.so\",\"modules\":[{\"name\": \"com_mesosphere_dcos_ClassicRPCAuthenticatee\"},{\"name\":\"com_mesosphere_dcos_http_Authenticatee\",\"parameters\":[{\"key\":\"jwt_exp_timeout\",\"value\":\"5mins\"},{\"key\":\"preemptive_refresh_duration\",\"value\":\"30mins\"}]}]}]}",
+    "DCOS_SERVICE_ACCOUNT_CREDENTIAL": "secrets/service-account.json",
+    "MESOS_MODULES": "{\"libraries\":[{\"file\":\"libmesos-bundle\/lib\/mesos\/libdcos_security.so\",\"modules\":[{\"name\": \"com_mesosphere_dcos_ClassicRPCAuthenticatee\", \"parameters\":[{\"key\":\"service_account_credential\",\"value\":\"file://secrets/service-account.json\"}]},{\"name\":\"com_mesosphere_dcos_http_Authenticatee\",\"parameters\":[{\"key\":\"service_account_credential\",\"value\":\"file://secrets/service-account.json\"},{\"key\":\"jwt_exp_timeout\",\"value\":\"5mins\"},{\"key\":\"preemptive_refresh_duration\",\"value\":\"30mins\"}]}]}]}",
     "MESOS_AUTHENTICATEE": "com_mesosphere_dcos_ClassicRPCAuthenticatee",
     "MESOS_HTTP_AUTHENTICATEE": "com_mesosphere_dcos_http_Authenticatee",
     {{/service.service_account_secret}}