job-info: return job id after lookup

Problem: If a user wishes to send multiple job info lookups in parallel,
they have to track which lookups belong to which job ids.  This can be
a tad inconvenient.

Solution: Return the job id in the lookup response along with the
information that was looked up.

Author: chu11

src/modules/job-info/lookup.c

@@ -160,6 +160,7 @@ static void info_lookup_continuation (flux_future_t *fall, void *arg)
     size_t index;
     json_t *key;
     json_t *o = NULL;
+    json_t *tmp = NULL;
     char *data = NULL;
 
     if (!l->allow) {
@@ -184,6 +185,12 @@ static void info_lookup_continuation (flux_future_t *fall, void *arg)
     if (!(o = json_object ()))
         goto enomem;
 
+    tmp = json_integer (l->id);
+    if (json_object_set_new (o, "id", tmp) < 0) {
+        json_decref (tmp);
+        goto enomem;
+    }
+
     json_array_foreach(l->keys, index, key) {
         flux_future_t *f;
         const char *keystr;