The problem is that Spring-Boot does not seem to play nice with the tomcat-plugin (A response that can get it working will steal the star!). As noted above you can reduce to just using the spring-boot...
buildscript {
  repositories {
    mavenLocal()
    mavenCentral()
  }
  dependencies {
    classpath("org.springframework.boot:spring-boot-gradle-plugin:1.1.1.RELEASE")
  }
}
apply plugin: 'war'
apply plugin: 'spring-boot'
war { baseName='itext' }
repositories {
  mavenLocal()
  mavenCentral()
}
dependencies {
  compile("org.springframework.boot:spring-boot-starter-web")
  providedRuntime("org.springframework.boot:spring-boot-starter-tomcat")
  testCompile("org.springframework.boot:spring-boot-starter-test")
}
If you do this, however, you will also need to change the Application.java to something like this....
package com.gleason.itext;
import java.util.Arrays;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.context.web.SpringBootServletInitializer;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.bind.annotation.PathVariable;
@Configuration
@ComponentScan
@EnableAutoConfiguration
public class Application extends SpringBootServletInitializer {
    public static void main(String[] args) {
        SpringApplication.run(applicationClass, args);
    }
    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        return application.sources(applicationClass);
    }
    private static Class<Application> applicationClass = Application.class;
}