SparkSession should be able to close a session while it is being opened

In HIVE-14162 we adding locks to SparkSessionImpl to support scenarios where we want to close the session due to a timeout. However, the locks remove the ability to close a session while it is being opened. This is important to allow cancelling of a session while it is being setup. This can be useful on busy clusters where there may not be enough YARN containers to setup the Spark Remote Driver.