Add explicit rackd image sync

- The import resources job can sometimes take much longer
  than expected seemingly because even though the rack
  controller has the image data, it doesn't report it.
  Rather than waiting for MAAS to resync the rack controller
  automatically, explicitly start an image sync on each rack
  controller that isn't synced

Change-Id: Ie3a8124db2266380420b1efa4aaec6e3aa3c2904

charts/maas/templates/bin/_import-boot-resources.sh.tpl

@@ -102,6 +102,8 @@ function check_for_rack_sync {
         if [[ $synced_ctlr == "true" && ! -z ${selected_imgs} ]]
         then
           sync_list=$(echo -e "${sync_list}\n${rack_id}" | sort | uniq)
+        else
+          maas ${ADMIN_USERNAME} rack-controller import-boot-images ${rack_id}
         fi
         if [[ $(echo -e "${rack_list}" | sort | uniq | grep -v '^$' ) == $(echo -e "${sync_list}" | sort | uniq | grep -v '^$') ]]
         then