ktest: Have POST_TEST run after the test has totally completed

The POST_TEST config is to be executed after a test has fully compeleted,
whether the test passed or failed. It currently is executed at the moment
that the test has been decided if it failed or not. As the test does other
clean ups, it isn't truly finished. Move the POST_TEST execution to after
all the test cleanups have been done.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>