Support ANSI color from gradle bootRun

Update the BootRunTask to record the state of the System.console() so
that it can be picked up later by AnsiOutput.

Fixes gh-747

spring-boot-tools/spring-boot-gradle-plugin/src/main/groovy/org/springframework/boot/gradle/run/BootRunTask.java

@@ -54,6 +54,10 @@ public class BootRunTask extends JavaExec {
 
 	@Override
 	public void exec() {
+		if(System.console() != null) {
+			// Record that the console is available here for AnsiOutput to detect later
+			this.getEnvironment().put("spring.output.ansi.console-available", true);
+		}
 		addResourcesIfNecessary();
 		super.exec();
 	}