Merge pull request #265 from harveyfeng/hive11-almost

Refactor SparkConf usage
Start the thread local hive session state before running commands to avoid a null pointer in the hive driver code.
Avoid restarting the session for each command
Start the session state before each query incase it has been cleared
Merge pull request #266 from marmbrus/fixSharkServerSessionState

Start the thread local hive session state before running commands to avoid a null pointer in the hive driver code..
Ignore JoinOperator for now.

It might not be too effective anyways, since we don't track Hive's version of stats.