Check for $HOME environment variable as well

Similar to our check for $USER, let's check for $HOME to allow
setting a custom home directory in weird build environments.

mkosi/user.py

@@ -56,7 +56,13 @@ def home(cls) -> Path:
  if cls.invoked_as_root and Path.cwd().is_relative_to("/home") and len(Path.cwd().parents) > 2:
  return list(Path.cwd().parents)[-3]
 
- return Path(f"~{cls.name()}").expanduser()
+ try:
+ return Path(pwd.getpwuid(cls.uid).pw_dir or "/")
+ except KeyError:
+ if not (home := os.getenv("HOME")):
+ die(f"Could not find home directory for UID {cls.uid}")
+
+ return Path(home)
 
  @classmethod
  @functools.lru_cache(maxsize=1)