Make sure loading_cache::stop() is always called where appropriate:
regardless whether the test failed or there was an exception during the test.
Otherwise a false-alarm use-after-free error may occur.
Fixes#2955
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
Message-Id: <1510625736-3109-1-git-send-email-vladz@scylladb.com>