osbuild.py: make StageFailed and AssemblerFailed consistent

This way they can both be used as ducks in an exception handler.

osbuild

@@ -34,7 +34,7 @@ if __name__ == "__main__":
         print()
         print(f"{RESET}{BOLD}{RED}Aborted{RESET}")
         sys.exit(130)
-    except osbuild.StageFailed as error:
+    except (osbuild.StageFailed, osbuild.AssemblerFailed) as error:
         print()
-        print(f"{RESET}{BOLD}{RED}{error.stage} failed with code {error.returncode}{RESET}")
+        print(f"{RESET}{BOLD}{RED}{error.name} failed with code {error.returncode}{RESET}")
         sys.exit(1)

osbuild.py

@@ -30,15 +30,15 @@ if not os.path.exists(f"{libdir}/stages"):
 
 
 class StageFailed(Exception):
-    def __init__(self, stage, returncode, output):
-        self.stage = stage
+    def __init__(self, name, returncode, output):
+        self.name = name
         self.returncode = returncode
         self.output = output
 
 
 class AssemblerFailed(Exception):
-    def __init__(self, assembler, returncode, output):
-        self.assembler = assembler
+    def __init__(self, name, returncode, output):
+        self.name = name
         self.returncode = returncode
         self.output = output