BaseTools/UPT:merge UPT Tool use Python2 and Python3

In UPT Tool,merge python2 and python3

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Zhiju.Fan <zhijux.fan@intel.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>

BaseTools/Source/Python/UPT/PomAdapter/InfPomAlignment.py

@@ -133,7 +133,7 @@ class InfPomAlignment(ModuleObject):
         #
         # Should only have one ArchString Item.
         #
-        ArchString = RecordSet.keys()[0]
+        ArchString = list(RecordSet.keys())[0]
         ArchList = GetSplitValueList(ArchString, ' ')
         ArchList = ConvertArchList(ArchList)
         HasCalledFlag = False