refactor(test): Have Microvm.screen_pid return int instead of str

A PID is an integer, so return it as one. Having it be a string means it
cannot be directly passed to things such as `os.kill`.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

tests/framework/microvm.py

@@ -490,9 +490,11 @@ def screen_log(self):
         return f"/tmp/screen-{self.screen_session}.log"
 
     @property
-    def screen_pid(self):
+    def screen_pid(self) -> Optional[int]:
         """Get the screen PID."""
-        return self._screen_pid
+        if self._screen_pid:
+            return int(self._screen_pid)
+        return None
 
     def pin_vmm(self, cpu_id: int) -> bool:
         """Pin the firecracker process VMM thread to a cpu list."""