Merge pull request #975 from cderici/juju-config-dir-fix-2.9

#975

#### Description

XDG_DATA_HOME is supposed to point to the parent directory for applications. We were incorrectly setting that as Juju config dir.

#### QA Steps

No operational logic changes. All CI tests need to pass.

#### Notes & Discussions

Thanks @jameinel for pointing this out!

juju/utils.py

@@ -45,18 +45,17 @@ def juju_config_dir():
     * ~/.local/share/juju
 
     """
-    # Check $JUJU_DATA first
-    config_dir = os.environ.get('JUJU_DATA', None)
+    # Set it to ~/.local/share/juju as default
+    config_dir = Path('~/.local/share/juju')
 
-    # Second option: $XDG_DATA_HOME for ~/.local/share
-    if not config_dir:
-        config_dir = os.environ.get('XDG_DATA_HOME', None)
+    # Check $JUJU_DATA
+    if juju_data := os.environ.get('JUJU_DATA'):
+        config_dir = Path(juju_data)
+    # Secondly check: $XDG_DATA_HOME for ~/.local/share
+    elif xdg_data_home := os.environ.get('XDG_DATA_HOME'):
+        config_dir = Path(xdg_data_home) / 'juju'
 
-    # Third option: just set it to ~/.local/share/juju
-    if not config_dir:
-        config_dir = '~/.local/share/juju'
-
-    return os.path.abspath(os.path.expanduser(config_dir))
+    return str(config_dir.expanduser().resolve())
 
 
 def juju_ssh_key_paths():