Standardize Build

The build now uses spring build conventions to simplify the build

Fixes gh-4284

samples/boot/insecure/build.gradle

@@ -1,12 +0,0 @@
-apply from: BOOT_SAMPLE_GRADLE
-
-springBoot {
-    mainClass = 'org.springframework.security.samples.InsecureApplication'
-}
-
-dependencies {
-    compile "org.springframework.boot:spring-boot-starter-web",
-            "org.springframework.boot:spring-boot-starter-thymeleaf"
-
-    testCompile "org.springframework.boot:spring-boot-starter-test"
-}

samples/boot/insecure/spring-security-samples-boot-insecure.gradle

@@ -0,0 +1,8 @@
+apply plugin: 'io.spring.convention.spring-sample-boot'
+
+dependencies {
+	compile 'org.springframework.boot:spring-boot-starter-thymeleaf'
+	compile 'org.springframework.boot:spring-boot-starter-web'
+
+	testCompile 'org.springframework.boot:spring-boot-starter-test'
+}