remove @ignore from tests that were waiting for b56 promotion

The following tests were added in b56 but could not be enable until
hotspot b56 was promoted :-

test/java/lang/instrument/FromShutdownHook.java
test/java/lang/management/ThreadMXBean/ThreadLists.java

The @ignore keyword can now be removed. In addition, FromShutdownHook needs
to be updated so that the agent is packaged into a jar file.