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/GenFds/GenFds.py

@@ -335,10 +335,10 @@ def main():
         """Display FV space info."""
         GenFds.DisplayFvSpaceInfo(FdfParserObj)
 
-    except FdfParser.Warning, X:
+    except FdfParser.Warning as X:
         EdkLogger.error(X.ToolName, FORMAT_INVALID, File=X.FileName, Line=X.LineNumber, ExtraData=X.Message, RaiseError=False)
         ReturnCode = FORMAT_INVALID
-    except FatalError, X:
+    except FatalError as X:
         if Options.debug is not None:
             import traceback
             EdkLogger.quiet(traceback.format_exc())