PilotBundle is not compatible with Python3

[hmiyake]

There are several issues in DIRAC/Resources/Computing/PilotBundle.py to run on python3 environment.

At first,

    compressedAndEncodedProxy = base64.b64encode(bz2.compress(proxy.dumpAllToString()["Value"])).decode()

needs to be something like

    compressedAndEncodedProxy = base64.b64encode(bz2.compress(proxy.dumpAllToString()["Value"].encode())).decode()

This code runs on only python3, however the pilot wrapper generated by the module may run on both python2 and python3.

  open('proxy', "w").write(bz2.decompress(base64.b64decode("{compressedAndEncodedProxy}")))
  open('{executable}', "w").write(bz2.decompress(base64.b64decode("{compressedAndEncodedExecutable}")))

needs to switch to 'wb' under python3 environment

except Exception as x:
  print >> sys.stderr, x
  sys.exit(-1)
cmd = "./{executable}"
print 'Executing: ', cmd

print above should be rewritten for both python2 and python3.