useful messages if required files are missing

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

managetests/utils.py

@@ -33,11 +33,13 @@ def is_root_valid(path):
     for dir in required_dirs:
         dir = path / dir
         if not (dir.exists() and dir.is_dir()):
+            print("The required directory %s does not exist" % dir)
             return False
 
     for file in required_files:
         file = path / file
         if not (file.exists() and file.is_file()):
+            print("The required file %s does not exist" % file)
             return False
 
     with (path / "version").open("r") as f: