salt: Avoid duplicating static pod manifests

When using `metalk8s.static_pod_managed`, we call `file.managed` behind
the scenes. This state does a lot of magic, including creating a
temporary file with the new contents before replacing the old file.
This temp file gets created **in the same directory** as the managed
file by default, so it gets picked up by `kubelet` as if it were
another static Pod to manage. If the replacement occurs too late,
`kubelet` may have already created another Pod for the temp file, and
may not be able to "remember" the old Pod, hence not cleaning it up.
This results in "rogue containers", which can create issues (e.g.
preventing new containers from binding some ports on the host).

This commit ensures we create the temp files in `/tmp` (unless
specified otherwise), which should prevent the aforementioned situation
from happening.

Fixes: #2840

salt/_states/metalk8s.py

@@ -1,5 +1,6 @@
 """Custom states for MetalK8s."""
 
+import tempfile
 import time
 import re
 
@@ -76,6 +77,7 @@ def static_pod_managed(name,
             context or {},
             config_digest=config_digest, metalk8s_version=metalk8s_version
         ),
+        tmp_dir=kwargs.pop("tmp_dir", tempfile.gettempdir()),
         **kwargs
     )