CAMEL-5974 Make defaultTaskExecutorType a read-only managed attribute; add a setter in JmsComponent; add a test for component-level defaultTaskExecutorType

git-svn-id: https://svn.apache.org/repos/asf/camel/branches/camel-2.10.x@1442800 13f79535-47bb-0310-9956-ffa450edef68