Fix ordering of property sources

When the bootstrap properties are added back into the main Environment
we have to be careful that any source that is already there (such as
one that was added in a Spring Boot EnvironmentPostProcessor) is not
replaced in the wrong order.

Fixes gh-90

spring-cloud-context/src/test/java/org/springframework/cloud/bootstrap/BootstrapOrderingSpringApplicationJsonIntegrationTests.java

@@ -0,0 +1,49 @@
+package org.springframework.cloud.bootstrap;
+
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.test.IntegrationTest;
+import org.springframework.boot.test.SpringApplicationConfiguration;
+import org.springframework.cloud.bootstrap.BootstrapOrderingSpringApplicationJsonIntegrationTests.Application;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.core.env.ConfigurableEnvironment;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@SpringApplicationConfiguration(classes = Application.class)
+@IntegrationTest("spring.cloud.bootstrap.name:json")
+public class BootstrapOrderingSpringApplicationJsonIntegrationTests {
+
+	@BeforeClass
+	public static void spikeJson() {
+		System.setProperty("SPRING_APPLICATION_JSON", "{\"message\":\"From JSON\"}");
+	}
+
+	@AfterClass
+	public static void unspikeJson() {
+		System.clearProperty("SPRING_APPLICATION_JSON");
+	}
+
+	@Autowired
+	private ConfigurableEnvironment environment;
+
+	@Test
+	public void bootstrapPropertiesExist() {
+		assertTrue(this.environment.getPropertySources()
+				.contains("spring.application.json"));
+		assertEquals("From JSON", this.environment.getProperty("message"));
+	}
+
+	@EnableAutoConfiguration
+	@Configuration
+	protected static class Application {
+	}
+
+}