Rename forallrepos plugin to for_all_repos

Comes closer to how the command is spelled. We can't uses dashes as that
is not compatible with the python syntax.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kas/plugins/__init__.py

@@ -39,13 +39,13 @@ def load():
         Import all kas plugins
     """
     from . import build
-    from . import forallrepos
+    from . import for_all_repos
     from . import checkout
     from . import shell
 
     register_plugins(build)
     register_plugins(checkout)
-    register_plugins(forallrepos)
+    register_plugins(for_all_repos)
     register_plugins(shell)