Add OPAL_VPID to unpacking

* Needed to properly read PMIx job data like the following
   - `OPAL_PMIX_LOCALLDR`
   - `OPAL_PMIX_RANK`
   - `OPAL_PMIX_GLOBAL_RANK`
   - `OPAL_PMIX_APPLDR`
   - `OPAL_PMIX_APP_RANK`

Signed-off-by: Joshua Hursey <jhursey@us.ibm.com>
(cherry picked from commit a557c4130c42a5a41aba5c08e606e7129d0bcb6d)

opal/dss/dss_load_unload.c

@@ -12,6 +12,7 @@
  * Copyright (c) 2014-2018 Intel, Inc. All rights reserved.
  * Copyright (c) 2015-2017 Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
+ * Copyright (c) 2018      IBM Corporation.  All rights reserved.
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -372,6 +373,10 @@ int opal_value_unload(opal_value_t *kv,
         *data = kv->data.ptr;
         break;
 
+    case OPAL_VPID:
+        memcpy(*data, &kv->data.name.vpid, sizeof(opal_vpid_t));
+        break;
+
     default:
         OPAL_ERROR_LOG(OPAL_ERR_NOT_SUPPORTED);
         return OPAL_ERR_NOT_SUPPORTED;