BaseTools: Handle the bytes and str difference

Deal with bytes and str is different, remove the unicode()
Using utcfromtimestamp instead of fromtimestamp.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Yunhua Feng <yunhuax.feng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

BaseTools/Source/Python/GenFds/Capsule.py

@@ -21,6 +21,7 @@ from CommonDataClass.FdfClass import CapsuleClassObject
 import Common.LongFilePathOs as os
 import subprocess
 from io import BytesIO
+from io import StringIO
 from Common.Misc import SaveFileOnChange
 from Common.Misc import PackRegistryFormatGuid
 import uuid
@@ -184,7 +185,7 @@ class Capsule (CapsuleClassObject) :
         #
         # The real capsule header structure is 28 bytes
         #
-        Header.write('\x00'*(HdrSize-28))
+        Header.write(b'\x00'*(HdrSize-28))
         Header.write(FwMgrHdr.getvalue())
         Header.write(Content.getvalue())
         #
@@ -246,7 +247,7 @@ class Capsule (CapsuleClassObject) :
     def GenCapInf(self):
         self.CapInfFileName = os.path.join(GenFdsGlobalVariable.FvDir,
                                    self.UiCapsuleName +  "_Cap" + '.inf')
-        CapInfFile = BytesIO() #open (self.CapInfFileName , 'w+')
+        CapInfFile = StringIO() #open (self.CapInfFileName , 'w+')
 
         CapInfFile.writelines("[options]" + T_CHAR_LF)