pmdaroot: add check for config.v2.json docker files

docker 1.10+ now uses a different config file.  Add a check and support
that new file.  Add example to qa and update appropriate output

qa/761.out

@@ -18,6 +18,36 @@ containers.cgroup
 No value(s) available!
 
 containers.engine
+    inst [N or "e137109040f53c67031325695ae541a3bf383c7b015af0fd718a412cc0f32da1"] value "docker"
+    inst [N or "e68c65472ffef4c1691c6c5d71327ce816231b2338753973550e7f5eda995fc9"] value "docker"
+
+containers.name
+    inst [N or "e137109040f53c67031325695ae541a3bf383c7b015af0fd718a412cc0f32da1"] value "tender_galileo"
+    inst [N or "e68c65472ffef4c1691c6c5d71327ce816231b2338753973550e7f5eda995fc9"] value "happy_hoover"
+
+containers.pid
+No value(s) available!
+
+containers.state.paused
+    inst [N or "e137109040f53c67031325695ae541a3bf383c7b015af0fd718a412cc0f32da1"] value 0
+    inst [N or "e68c65472ffef4c1691c6c5d71327ce816231b2338753973550e7f5eda995fc9"] value 0
+
+containers.state.restarting
+    inst [N or "e137109040f53c67031325695ae541a3bf383c7b015af0fd718a412cc0f32da1"] value 0
+    inst [N or "e68c65472ffef4c1691c6c5d71327ce816231b2338753973550e7f5eda995fc9"] value 0
+
+containers.state.running
+    inst [N or "e137109040f53c67031325695ae541a3bf383c7b015af0fd718a412cc0f32da1"] value 0
+    inst [N or "e68c65472ffef4c1691c6c5d71327ce816231b2338753973550e7f5eda995fc9"] value 0
+
+== done
+
+== Checking values for active containers
+
+containers.cgroup
+No value(s) available!
+
+containers.engine
     inst [N or "781d21edbb014736f7fb4e1412ee55c5564c91ce0647be4879a7c547e6ebc1af"] value "docker"
     inst [N or "d4999f7c6d639c837c03634ab2bc51daa5b35fce1bf1e9f56ee9f8342fafa2ec"] value "docker"
 

src/pmdas/root/docker.c

@@ -351,6 +351,29 @@ docker_values_parse(FILE *fp, const char *name, container_t *values)
     return sts;
 }
 
+/* docker decided to not only change the config file json pointer layout, but
+ * also the filename in which the config resides.  Check which version is being used.
+ */
+int determine_docker_version(container_engine_t *dp, const char *name, char *buf, size_t bufsize)
+{
+    FILE *fp;
+
+    /* we go with version two first, because v1 config files may not
+     * always be cleaned up after the upgrade to v2.
+     */
+    snprintf(buf, bufsize, "%s/%s/config.v2.json", dp->path, name);
+    if ((fp = fopen(buf, "r")) != NULL) {
+	fclose(fp);
+	return 2;
+    }
+    snprintf(buf, bufsize, "%s/%s/config.json", dp->path, name);
+    if ((fp = fopen(buf, "r")) != NULL) {
+	fclose(fp);
+	return 1;
+    }
+    return -oserror();
+}
+
 /*
  * Extract critical information (PID1, state) for a named container.
  * Name here is the unique identifier we've chosen to use for Docker
@@ -364,7 +387,10 @@ docker_value_refresh(container_engine_t *dp,
     FILE	*fp;
     char	path[MAXPATHLEN];
 
-    snprintf(path, sizeof(path), "%s/%s/config.json", dp->path, name);
+    sts = determine_docker_version(dp, name, path, sizeof(path));
+    if (sts < 0)
+	return sts;
+
     if (!docker_values_changed(path, values))
 	return 0;
     if (pmDebug & DBG_TRACE_ATTR)