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/Workspace/MetaFileTable.py

@@ -63,7 +63,7 @@ class MetaFileTable(Table):
                 # update the timestamp in database
                 self._FileIndexTable.SetFileTimeStamp(self.IdBase, TimeStamp)
                 return False
-        except Exception, Exc:
+        except Exception as Exc:
             EdkLogger.debug(EdkLogger.DEBUG_5, str(Exc))
             return False
         return True
@@ -250,7 +250,7 @@ class PackageTable(MetaFileTable):
                 if comment.startswith("@Expression"):
                     comment = comment.replace("@Expression", "", 1)
                     expressions.append(comment.split("|")[1].strip())
-        except Exception, Exc:
+        except Exception as Exc:
             ValidType = ""
             if oricomment.startswith("@ValidRange"):
                 ValidType = "@ValidRange"