fix issue 682

I discover a big issue in the maven plugin in flyway 2.3.1, you cannot set any boolean property with a java system property in command line (like -Dflyway.outOfOrder=true).

i did some debuging and the method getBooleanProperty got a very small bug.
Boolean.getBoolean(systemPropertyValue) should be  Boolean.getBoolean(systemPropertyName)


PS: i try with flyway 2.1.1 and its working,
i had a unit test