Stopped safe_remove attempting to unlink dirs

Previously safe_remove would attempt to unlink a path
Before attempting to remove it if it was a dir

Now it checks for a dir before that step

buildstream/utils.py

@@ -35,6 +35,7 @@ import tempfile
 import itertools
 import functools
 from contextlib import contextmanager
+from stat import S_ISDIR
 
 import psutil
 
@@ -328,25 +329,25 @@ def safe_remove(path):
     Raises:
        UtilError: In the case of unexpected system call failures
     """
-    if os.path.lexists(path):
+    if not S_ISDIR(os.lstat(path).st_mode):
 
         # Try to remove anything that is in the way, but issue
         # a warning instead if it removes a non empty directory
         try:
             os.unlink(path)
+            return True
         except OSError as e:
-            if e.errno != errno.EISDIR:
-                raise UtilError("Failed to remove '{}': {}"
-                                .format(path, e))
-
-            try:
-                os.rmdir(path)
-            except OSError as e:
-                if e.errno == errno.ENOTEMPTY:
-                    return False
-                else:
-                    raise UtilError("Failed to remove '{}': {}"
-                                    .format(path, e))
+            raise UtilError("Failed to remove '{}': {}"
+                            .format(path, e))
+
+    try:
+        os.rmdir(path)
+    except OSError as e:
+        if e.errno == errno.ENOTEMPTY:
+            return False
+        else:
+            raise UtilError("Failed to remove '{}': {}"
+                            .format(path, e))
 
     return True