MINOR; Update merge script to work against Python3
MINOR; Update merge script to work against Python3

Made the following changes so that it works in Python3:

1. Use `print()` instead of `print`
2. Use urllib instead of urllib2
3. Decode all of the cmd outputs from binary to string using UTF-8
4. Use `input` instead of `raw_input`
5. Use `next()` on the iterator returned by `filter()` instead `__get_item__()`
6. Fix any error returned by `pylint`.

Author: José Armando García Sancio <jsancio@gmail.com>

Reviewers: David Jacot <djacot@confluent.io>

Closes #11536 from jsancio/minor-merge-pr-script

apache/kafka,lindong28/kafka,TiVo/kafka,TiVo/kafka,guozhangwang/kafka,TiVo/kafka,lindong28/kafka,guozhangwang/kafka,lindong28/kafka,guozhangwang/kafka,apache/kafka,apache/kafka,lindong28/kafka,TiVo/kafka,apache/kafka,guozhangwang/kafka