camel-test - Make it easy to provider override properties from unit tests

When unit testing you may use properties from osgi config admin, or external resources and whatnot.

We should make it easier to provide a java.util.Properties from the unit test source code.

See nabble
http://camel.465427.n5.nabble.com/Overwrite-blueprint-properties-in-camel-blueprint-tests-tp5710948.html