Add autoconfig support for Flyway migrations

Flyway starts up with its default settings if it is on the classpath.
You can also ask Boot to barf if the migration scripts are missing.

Fixes gh-730

spring-boot-samples/spring-boot-sample-flyway/src/main/resources/db/migrations/V1__init.sql

@@ -0,0 +1,7 @@
+CREATE TABLE PERSON (
+	id INTEGER GENERATED BY DEFAULT AS IDENTITY,
+	first_name varchar(255) not null,
+	last_name varchar(255) not null
+);
+
+insert into PERSON (first_name, last_name) values ('Dave', 'Syer');