GH-3090: Add logout() to FtpSession.close()`

Fixes #3090

Without `logout()` the FTP session is not closed at all,
but just the connection is closed.
Some FTP servers close those sessions eventually anyway, but some just
leak with resources.

**Cherry-pick to 5.1.x & 4.3.x**

Author: artembilan

spring-integration-ftp/src/main/java/org/springframework/integration/ftp/session/FtpSession.java

@@ -153,6 +153,7 @@ public void close() {
 					}
 				}
 			}
+			this.client.logout();
 			this.client.disconnect();
 		}
 		catch (Exception e) {
@@ -196,7 +197,6 @@ public boolean rmdir(String directory) throws IOException {
 		return this.client.removeDirectory(directory);
 	}
 
-
 	@Override
 	public boolean exists(String path) throws IOException {
 		Assert.hasText(path, "'path' must not be empty");

spring-integration-ftp/src/test/java/org/springframework/integration/ftp/session/SessionFactoryTests.java

@@ -45,14 +45,15 @@
  * @author Oleg Zhurakousky
  * @author Gunnar Hillert
  * @author Gary Russell
+ * @author Artem Bilan
  *
  */
 @SuppressWarnings({"rawtypes", "unchecked"})
 public class SessionFactoryTests {
 
 
 	@Test
-	public void testTimeouts() throws Exception {
+	public void testFtpClientInteraction() throws Exception {
 		final FTPClient client = mock(FTPClient.class);
 		DefaultFtpSessionFactory sessionFactory = new DefaultFtpSessionFactory() {
 
@@ -67,10 +68,15 @@ protected FTPClient createClientInstance() {
 		sessionFactory.setDataTimeout(789);
 		doReturn(200).when(client).getReplyCode();
 		doReturn(true).when(client).login("foo", null);
-		sessionFactory.getSession();
+		FtpSession session = sessionFactory.getSession();
 		verify(client).setConnectTimeout(123);
 		verify(client).setDefaultTimeout(456);
 		verify(client).setDataTimeout(789);
+
+		session.close();
+
+		verify(client).logout();
+		verify(client).disconnect();
 	}
 
 	@Test