Add template creation test, --skip-editor option (#11970)

* Add template creation test
* Added --skip-editor option to "spack create": normally
  "spack create" opens an editor for the user after generating a
  package file; when the --skip-editor option is used, "spack create"
  only generates the package file and does not open an editor
* Added --skip-editor option to bash completion

share/spack/spack-completion.bash

@@ -352,7 +352,7 @@ function _spack_create {
     if $list_options
     then
         compgen -W "-h --help --keep-stage -n --name -t --template -r --repo
-                    -N --namespace -f --force" -- "$cur"
+                    -N --namespace -f --force --skip-editor" -- "$cur"
     fi
 }