[SPARK-11270][STREAMING] Add improved equality testing for TopicAndPartition...

[SPARK-11270][STREAMING] Add improved equality testing for TopicAndPartition from the Kafka Streaming API

jerryshao tdas

I know this is kind of minor, and I know you all are busy, but this brings this class in line with the `OffsetRange` class, and makes tests a little more concise.

Instead of doing something like:
```
assert topic_and_partition_instance._topic == "foo"
assert topic_and_partition_instance._partition == 0
```

You can do something like:
```
assert topic_and_partition_instance == TopicAndPartition("foo", 0)
```

Before:
```
>>> from pyspark.streaming.kafka import TopicAndPartition
>>> TopicAndPartition("foo", 0) == TopicAndPartition("foo", 0)
False
```

After:
```
>>> from pyspark.streaming.kafka import TopicAndPartition
>>> TopicAndPartition("foo", 0) == TopicAndPartition("foo", 0)
True
```

I couldn't find any tests - am I missing something?

Author: Nick Evans <me@nicolasevans.org>

Closes #9236 from manygrams/topic_and_partition_equality.