Move services/shell to services/service_manager

services/service_manager/tests/shutdown/shutdown_unittest_manifest.json

 {
   "manifest_version":  1,
   "name": "service:shutdown_unittest",
   "display_name": "Shutdown Unittest",
   "capabilities": {
     "required": {
       "service:shell": [ "shell:service_manager" ],
       "service:shutdown_client": [
         "shutdown_unittest:shutdown_test_client_controller"
       ],
       "service:shutdown_service": [ "shutdown_unittest:shutdown_test_service" ]
     }
   }
 }