JSCS Cleanup - style cleanup for modal factory

Per the style guide:

Factory and service should both just be .service.js

https://github.com/johnpapa/angular-styleguide#style-y121

Notice the comment:
/**
 * recommended
 */
// services/factories
logger.service.js
logger.service.spec.js

And discussion here:

https://review.openstack.org/#/c/182243
https://review.openstack.org/#/c/195660

Change-Id: I361f38f0fb1989190fe1b3e75f224d4c46aafbf4
Partially-Implements: blueprint jscs-cleanup

doc/source/topics/angularjs.rst

@@ -72,7 +72,7 @@ component:
 
   horizon/static/framework/widgets/modal/
   ├── modal.controller.js
-  ├── modal.factory.js
+  ├── modal.service.js
   ├── modal.module.js
   ├── modal.spec.js
   └── simple-modal.html

doc/source/topics/javascript_testing.rst

@@ -104,7 +104,7 @@ File tree:
 
   horizon/static/framework/widgets/modal
   ├── modal.controller.js
-  ├── modal.factory.js
+  ├── modal.service.js
   ├── modal.module.js
   └── modal.spec.js
 
@@ -116,7 +116,7 @@ Lines added to ``horizon/test/jasmine/jasmine_tests.py``:
       ...
       'framework/widgets/modal/modal.module.js',
       'framework/widgets/modal/modal.controller.js',
-      'framework/widgets/modal/modal.factory.js',
+      'framework/widgets/modal/modal.service.js',
       ...
     ]