config: return passed in tool by default

The tools in the tools key can either be a single string with the binary
name or a complete path to a binary. This works for every tool expect
for qemu since drivers can provide a fallback to the default tool.
However qemu currently requires the user to supply the full binary path,
which is unintuitive.

Instead return the originally requested tool-name if no specialized path
is found. And return the simple unexpanded path if a local tool with the
same name can't be found.

Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>
(cherry picked from commit 552a42c)
Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>

Author: Emantor

labgrid/config.py

@@ -98,9 +98,14 @@ def get_tool(self, tool):
         """
         try:
             path = str(self.data['tools'][tool])
-            return self.resolve_path(path)
         except KeyError:
-            return None
+            return tool
+
+        resolved = self.resolve_path(path)
+        if os.path.exists(resolved):
+            return resolved
+
+        return path
 
     def get_image_path(self, kind):
         """Retrieve an entry from the images subkey