Style cleanups, use nvlist_empty, variable renames, early variable initialisation.

*** 19,28 ****
--- 19,29 ----
   * CDDL HEADER END
   */
  
  /*
   * Copyright (c) 2012 by Delphix. All rights reserved.
+  * Copyright (c) 2013 Steven Hartland. All rights reserved.
   */
  
  /*
   * zhack is a debugging tool that can write changes to ZFS pool using libzpool
   * for testing purposes. Altering pools with zhack is unsupported and may
*** 151,161 ****
          if ((sepp = strpbrk(g_pool, "/@")) != NULL)
                  *sepp = '\0';
          g_importargs.poolname = g_pool;
          pools = zpool_search_import(g_zfs, &g_importargs);
  
!         if (pools == NULL || nvlist_next_nvpair(pools, NULL) == NULL) {
                  if (!g_importargs.can_be_active) {
                          g_importargs.can_be_active = B_TRUE;
                          if (zpool_search_import(g_zfs, &g_importargs) != NULL ||
                              spa_open(target, &spa, FTAG) == 0) {
                                  fatal("cannot import '%s': pool is active; run "
--- 152,162 ----
          if ((sepp = strpbrk(g_pool, "/@")) != NULL)
                  *sepp = '\0';
          g_importargs.poolname = g_pool;
          pools = zpool_search_import(g_zfs, &g_importargs);
  
!         if (nvlist_empty(pools)) {
                  if (!g_importargs.can_be_active) {
                          g_importargs.can_be_active = B_TRUE;
                          if (zpool_search_import(g_zfs, &g_importargs) != NULL ||
                              spa_open(target, &spa, FTAG) == 0) {
                                  fatal("cannot import '%s': pool is active; run "