enable less sourcemaps, add cleanup for npm cmds run with --prefix

awx/ui/grunt-tasks/clean.js

@@ -1,4 +1,6 @@
 module.exports = {
+    options: { force: true },
     static: 'static/*',
-    coverage: 'coverage/*'
+    coverage: 'coverage/*',
+    tmp: '../../tmp'
 };

awx/ui/grunt-tasks/less.js

@@ -11,7 +11,10 @@ module.exports = {
                 'client/legacy-styles/*.less',
                 'client/src/**/*.less',
             ]
-        }]
+        }],
+        options: {
+            sourceMap: true
+        }
     },
 
     prod: {
@@ -23,7 +26,6 @@ module.exports = {
         },
         options: {
             compress: true,
-
         }
     }
 };