Clean ant lib folder before build

Update `spring-boot-smoke-test-ant` so that the ant lib folder is always
cleaned. Prior to this commit, it was possible for the folder to contain
stale artifacts.

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-ant/build.gradle

@@ -51,6 +51,7 @@ task antRun(type: JavaExec) {
 	dependsOn syncTestRepository, configurations.antDependencies
 	classpath = configurations.antDependencies;
 	main = "org.apache.tools.ant.launch.Launcher"
+	args = [ "clean", "build" ]
 	systemProperties = [
 		"ant-spring-boot.version" : version,
 		"projectDir": project.layout.projectDirectory

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-ant/build.xml

@@ -38,6 +38,7 @@
 
 	<target name="clean" description="cleans all created files/dirs">
 		<delete dir="target" />
+		<delete dir="${lib.dir}" />
 	</target>
 
 	<target name="build" depends="compile">
@@ -48,6 +49,7 @@
 			</spring-boot:lib>
 		</spring-boot:exejar>
 	</target>
+
 	<!-- Manual equivalent of the build target -->
 	<target name="manual" depends="compile">
 		<jar destfile="target/${ant.project.name}-${ant-spring-boot.version}.jar" compress="false">