[SPARK-10071] [STREAMING] Output a warning when writing QueueInputDStream and...

[SPARK-10071] [STREAMING] Output a warning when writing QueueInputDStream and throw a better exception when reading QueueInputDStream

Output a warning when serializing QueueInputDStream rather than throwing an exception to allow unit tests use it. Moreover, this PR also throws an better exception when deserializing QueueInputDStream to make the user find out the problem easily. The previous exception is hard to understand: https://issues.apache.org/jira/browse/SPARK-8553

Author: zsxwing <zsxwing@gmail.com>

Closes #8624 from zsxwing/SPARK-10071 and squashes the following commits:

847cfa8 [zsxwing] Output a warning when writing QueueInputDStream and throw a better exception when reading QueueInputDStream