Disable JspServlet's development mode by default

This commit switches off the auto-configured JspServlet's
development mode by default. Development mode is then switched on
when DevTools is on the class path.

Closes gh-7039

spring-boot-devtools/pom.xml

@@ -117,6 +117,11 @@
 			<artifactId>tomcat-embed-core</artifactId>
 			<scope>test</scope>
 		</dependency>
+		<dependency>
+			<groupId>org.apache.tomcat.embed</groupId>
+			<artifactId>tomcat-embed-jasper</artifactId>
+			<scope>test</scope>
+		</dependency>
 		<dependency>
 			<groupId>org.eclipse.jetty.websocket</groupId>
 			<artifactId>websocket-client</artifactId>