Don't eagerly initialize FactoryBeans

Fix `EmbeddedServletContainerAutoConfiguration` so that it does not
accidentally eagerly initialize factory beans.

Fixes gh-306

spring-boot-autoconfigure/src/test/resources/early-init-test.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<beans xmlns="http://www.springframework.org/schema/beans"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
+
+	<bean id="earlyInit" class="org.springframework.boot.autoconfigure.EarlyInitFactoryBean" >
+		<property name="propertyFromConfig" value="${foo}" />
+	</bean>
+
+</beans>