Fix session timeout default value

Update DEFAULT_SESSION_TIMEOUT to use TimeUnit.MINUTES.toSeconds(30)
rather than TimeUnit.SECONDS.toMinutes(30) which would always return
0.

See gh-2084
(cherry picked from commit b33bbd56)

spring-boot/src/main/java/org/springframework/boot/context/embedded/AbstractConfigurableEmbeddedServletContainer.java

@@ -37,8 +37,8 @@ import org.springframework.util.Assert;
 public abstract class AbstractConfigurableEmbeddedServletContainer implements
 		ConfigurableEmbeddedServletContainer {
 
-	private static final int DEFAULT_SESSION_TIMEOUT = (int) TimeUnit.SECONDS
+	private static final int DEFAULT_SESSION_TIMEOUT = (int) TimeUnit.MINUTES
-			.toMinutes(30);
+			.toSeconds(30);
 
 	private String contextPath = "";
 

spring-boot/src/test/java/org/springframework/boot/context/embedded/AbstractEmbeddedServletContainerFactoryTests.java

@@ -530,6 +530,11 @@ public abstract class AbstractEmbeddedServletContainerFactoryTests {
 				equalTo("test"));
 	}
 
+	@Test
+	public void defaultSessionTimeout() throws Exception {
+		assertThat(getFactory().getSessionTimeout(), equalTo(30 * 60));
+	}
+
 	protected String getLocalUrl(String resourcePath) {
 		return getLocalUrl("http", resourcePath);
 	}