Merge pull request #3174 from vvoland/volume-subpath

api: Support Subpath volume option

Author: dperny

api/api.pb.txt

@@ -2729,6 +2729,16 @@ file {
         type_name: ".docker.swarmkit.v1.Driver"
         json_name: "driverConfig"
       }
+      field {
+        name: "subpath"
+        number: 4
+        label: LABEL_OPTIONAL
+        type: TYPE_STRING
+        options {
+          65004: "Subpath"
+        }
+        json_name: "subpath"
+      }
       nested_type {
         name: "LabelsEntry"
         field {