Fix Brussels Build

- Update Spring IO plugin to resolve binary incompatability for tests
- Update Dependency Management Plugin which is required for Spring IO
  plugin update
- Update to Spring Boot 1.5.0.RC1. Necessary because new dependency
  management plugin does not work with Boot 1.4.x

Fixes gh-708

samples/httpsession-jdbc-boot/build.gradle

@@ -1,6 +1,7 @@
 buildscript {
 	repositories {
 		mavenCentral()
+		maven { url "https://repo.spring.io/milestone" }
 	}
 	dependencies {
 		classpath("org.springframework.boot:spring-boot-gradle-plugin:$springBootVersion")