update managetests.json for to the new style

Signed-off-by: Mattia Rizzolo <mattia@debian.org>

managetests.json

 {
     "build": [
-        ["invoke", "build"]
-    ],
-    "before_install": [
-        ["mkdir", "{{base}}/data"],
-        ["virtualenv", "-p", "python3", "{{base}}/env"]
-    ],
-    "install": [
-        {
-            "artifacts": "build/packages/*.whl",
-            "command": ["{{base}}/env/bin/pip", "install", "{{artifact}}"]
-        }
+        ["./run", "build_scss"],
+        ["./run", "init", "{{base}}/data"]
     ],
     "run": [
-        "{{base}}/env/bin/uitwww", "run", "-g", "{{gunicorn_config_file}}",
+        "{{base}}/build/run", "run",
+        "-g", "{{gunicorn_config_file}}",
         "{{base}}/data"
     ]
 }