Move TestEnvironment from providing a SparkContext to providing a SparkSession

[lossyrob]

In geotrellis.spark.testkit.TestEnvironment, we provide a SparkContext. We should provide a SparkSession; you can get a spark context from a spark session, but can't start a spark session after the spark context is already created, without some deprecated code.

[metasim]

This is how I handle it in a subclass to TestEnvironment. As you state, causes a deprecation warning, which I'd love to get rid of:

  override implicit def sc: SparkContext = { _sc.setLogLevel("ERROR"); _sc }

  lazy val sqlContext: SQLContext = SQLContext.getOrCreate(_sc)

  implicit lazy val spark = sqlContext.sparkSession