Fixed couple errors after rebase

Also added unit tests for `Futures#asCompletionException()`.

Author: lutovich

driver/src/main/java/org/neo4j/driver/internal/ExplicitTransaction.java

@@ -371,13 +371,13 @@ private BiFunction<Void,Throwable,Void> handleCommitOrRollback( Throwable cursor
         {
             if ( cursorFailure != null && commitOrRollbackError != null )
             {
-                Throwable cause1 = completionErrorCause( cursorFailure );
-                Throwable cause2 = completionErrorCause( commitOrRollbackError );
+                Throwable cause1 = Futures.completionExceptionCause( cursorFailure );
+                Throwable cause2 = Futures.completionExceptionCause( commitOrRollbackError );
                 if ( cause1 != cause2 )
                 {
                     cause1.addSuppressed( cause2 );
                 }
-                throw new CompletionException( cause1 );
+                throw Futures.asCompletionException( cause1 );
             }
             else if ( cursorFailure != null )
             {

driver/src/test/java/org/neo4j/driver/internal/util/FuturesTest.java

@@ -335,14 +335,29 @@ public void shouldGetCauseFromCompletionException()
         RuntimeException error = new RuntimeException( "Hello" );
         CompletionException completionException = new CompletionException( error );
 
-        assertEquals( error, Futures.completionErrorCause( completionException ) );
+        assertEquals( error, Futures.completionExceptionCause( completionException ) );
     }
 
     @Test
     public void shouldReturnSameExceptionWhenItIsNotCompletionException()
     {
         RuntimeException error = new RuntimeException( "Hello" );
 
-        assertEquals( error, Futures.completionErrorCause( error ) );
+        assertEquals( error, Futures.completionExceptionCause( error ) );
+    }
+
+    @Test
+    public void shouldWrapWithCompletionException()
+    {
+        RuntimeException error = new RuntimeException( "Hello" );
+        CompletionException completionException = Futures.asCompletionException( error );
+        assertEquals( error, completionException.getCause() );
+    }
+
+    @Test
+    public void shouldKeepCompletionExceptionAsIs()
+    {
+        CompletionException error = new CompletionException( new RuntimeException( "Hello" ) );
+        assertEquals( error, Futures.asCompletionException( error ) );
     }
 }