storage: Add timeout for iscsi volume's stable path discovery

It might need some time till the LUN's stable path shows up on
initiator host, and although the time window is not foreseeable,
as a better than nothing fix, this patch adds timeout for the
stable path discovery process.
(cherry picked from commit de7f0774)

src/storage/storage_backend.c

@@ -1347,6 +1347,7 @@ virStorageBackendStablePath(virStoragePoolObjPtr pool,
     struct dirent *dent;
     char *stablepath;
     int opentries = 0;
+    int retry = 0;
 
     /* Short circuit if pool has no target, or if its /dev */
     if (pool->def->target.path == NULL ||
@@ -1355,7 +1356,7 @@ virStorageBackendStablePath(virStoragePoolObjPtr pool,
         goto ret_strdup;
 
     /* Skip whole thing for a pool which isn't in /dev
-     * so we don't mess will filesystem/dir based pools
+     * so we don't mess filesystem/dir based pools
      */
     if (!STRPREFIX(pool->def->target.path, "/dev"))
         goto ret_strdup;
@@ -1384,8 +1385,12 @@ virStorageBackendStablePath(virStoragePoolObjPtr pool,
     /* The pool is pointing somewhere like /dev/disk/by-path
      * or /dev/disk/by-id, so we need to check all symlinks in
      * the target directory and figure out which one points
-     * to this device node
+     * to this device node.
+     *
+     * And it might need some time till the stabe path shows
+     * up, so add timeout to retry here.
      */
+ retry:
     while ((dent = readdir(dh)) != NULL) {
         if (dent->d_name[0] == '.')
             continue;
@@ -1406,6 +1411,11 @@ virStorageBackendStablePath(virStoragePoolObjPtr pool,
         VIR_FREE(stablepath);
     }
 
+    if (++retry < 100) {
+        usleep(100 * 1000);
+        goto retry;
+    }
+
     closedir(dh);
 
  ret_strdup: