[SPARK-4037][SQL] Removes the SessionState instance created in HiveThriftServer2

`HiveThriftServer2` creates a global singleton `SessionState` instance and overrides `HiveContext` to inject the `SessionState` object. This messes up `SessionState` initialization and causes problems.

This PR replaces the global `SessionState` with `HiveContext.sessionState` to avoid the initialization conflict. Also `HiveContext` reuses existing started `SessionState` if any (this is required by `SparkSQLCLIDriver`, which uses specialized `CliSessionState`).

Author: Cheng Lian <lian@databricks.com>

Closes #2887 from liancheng/spark-4037 and squashes the following commits:

8446675 [Cheng Lian] Removes redundant Driver initialization
a28fef5 [Cheng Lian] Avoid starting HiveContext.sessionState multiple times
49b1c5b [Cheng Lian] Reuses existing started SessionState if any
3cd6fab [Cheng Lian] Fixes SPARK-4037