CDAP-693 Adding the ability to run hive queries on streams.

This includes various changes to make this possible.

Streams are now created when an application is deployed
instead of lazily created when the first event is written to it.
If explore is enabled when a stream is created, an external
hive table is created using a custom HiveStorageHandler for
streams. This required some refactoring around the stream input
format, as our mapreduce code uses the newer mapreduce apis, but
the hive code uses the old mapred apis.
Hive basically does a prefix match on the table location and location of mapper input, so I think the raw location without generation should be fine, as long as the StreamInputFormat only returns input splits for the current generation. I will check whether it does that or not, but it should be there, since that seems like the correct behavior for mapreduce jobs.