BaseTools: Handle the bytes and str difference

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

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/Pkcs7Sign/Pkcs7Sign.py

@@ -122,7 +122,7 @@ if __name__ == '__main__':
   if Process.returncode != 0:
     print('ERROR: Open SSL command not available.  Please verify PATH or set OPENSSL_PATH')
     sys.exit(Process.returncode)
-  print(Version[0])
+  print(Version[0].decode())
 
   #
   # Read input file into a buffer and save input filename