Use logical working directory, not resolving symlinks

When running from a symlinked subfolder, os.getcwd() and Path.cwd()
return the real path with all all symlinks resolved.
This resulted in the workspace root to be found w.r.t. the real path
instead the actual logical one.

Author: rhaschke

Diff for: colcon_top_level_workspace/argument_parser.py

@@ -84,7 +84,10 @@ def is_root(path):
             return True
         return all([(path / folder).is_dir() for folder in ["log", "build", "install"]])
 
-    path = Path.cwd()
+    # get logical working directory (with symlinks not resolved)
+    path = os.environ.get("PWD")
+
+    path = Path(path) if path is not None else Path.cwd()
     _root_path = path
     anchor = Path(path.anchor)
     while True: