BaseTools: Refactor python except statements

Convert "except ... ," to "except ... as" to be compatible with python3.
Based on "futurize -f lib2to3.fixes.fix_except"

Contributed-under: TianoCore Contribution Agreement 1.1
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>

BaseTools/Source/Python/TargetTool/TargetTool.py

@@ -253,7 +253,7 @@ if __name__ == '__main__':
             FileHandle.RWFile('#', '=', 0)
         else:
             FileHandle.RWFile('#', '=', 1)
-    except Exception, e:
+    except Exception as e:
         last_type, last_value, last_tb = sys.exc_info()
         traceback.print_exception(last_type, last_value, last_tb)