Fix CachedTableSuite tests.

Author: JoshRosen

sql/core/src/test/scala/org/apache/spark/sql/CachedTableSuite.scala

@@ -46,7 +46,9 @@ class CachedTableSuite extends QueryTest with SQLTestUtils with SharedSQLContext
   }
 
   def isMaterialized(rddId: Int): Boolean = {
-    sparkContext.env.blockManager.get(RDDBlockId(rddId, 0)).nonEmpty
+    val maybeBlock = sparkContext.env.blockManager.get(RDDBlockId(rddId, 0))
+    maybeBlock.foreach(_ => sparkContext.env.blockManager.release(RDDBlockId(rddId, 0)))
+    maybeBlock.nonEmpty
   }
 
   test("withColumn doesn't invalidate cached dataframe") {

sql/hive/src/test/scala/org/apache/spark/sql/hive/CachedTableSuite.scala

@@ -40,7 +40,9 @@ class CachedTableSuite extends QueryTest with TestHiveSingleton {
   }
 
   def isMaterialized(rddId: Int): Boolean = {
-    sparkContext.env.blockManager.get(RDDBlockId(rddId, 0)).nonEmpty
+    val maybeBlock = sparkContext.env.blockManager.get(RDDBlockId(rddId, 0))
+    maybeBlock.foreach(_ => sparkContext.env.blockManager.release(RDDBlockId(rddId, 0)))
+    maybeBlock.nonEmpty
   }
 
   test("cache table") {