Move integration tests => src/test

This commit eliminates the 'integration-tests' subproject in favor of
managing these sources under the root project's own 'src' directory.

This helps to avoid special-case handling for integration-tests in the
Gradle build, e.g. avoiding publication of jars to Artifactory /
Maven Central.

It is also semantically more correct. This is not a Spring Framework
subproject so much as it is a collection of integration tests that
span functionality across many subprojects. In this way, it makes
sense to place them directly under the root project.

Issue: SPR-8116

src/test/resources/org/springframework/transaction/annotation/enable-caching.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xmlns:cache="http://www.springframework.org/schema/cache"
+	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
+		http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache.xsd">
+
+	<cache:annotation-driven/>
+
+</beans>

src/test/resources/org/springframework/util/testlog4j.properties

@@ -0,0 +1,2 @@
+log4j.rootCategory=DEBUG, mock
+log4j.appender.mock=org.springframework.util.MockLog4jAppender

src/test/resources/org/springframework/web/util/testlog4j.properties

@@ -0,0 +1,2 @@
+log4j.rootCategory=DEBUG, mock
+log4j.appender.mock=org.springframework.util.MockLog4jAppender