manage/Gruntfile.js: Add yeoman.dist/images to assetDirs

Without this, images are renamed, but the references to them in the CSS
aren't updated correctly, which prevents the SUSE logo in the footer
displaying.  For further discussion, see
yeoman/yeoman#824 (comment)

It's curious that this fix doesn't seem to be necessary for
dashboard/Gruntfile.js (are the files there not being renamed by rev?)

Signed-off-by: Tim Serong <tserong@suse.com>
(cherry picked from commit 71b1cd791fe64aedc8c1cb766f37687075320e4e)

manage/Gruntfile.js

@@ -255,7 +255,7 @@ module.exports = function (grunt) {
       html: ['<%= yeoman.dist %>/{,*/}*.html'],
       css: ['<%= yeoman.dist %>/styles/{,*/}*.css'],
       options: {
-        assetsDirs: ['<%= yeoman.dist %>']
+        assetsDirs: ['<%= yeoman.dist %>', '<%= yeoman.dist %>/images' ]
       }
     },