Problem: Creates too many encryption keys.

While you are at it: we discussed before that the test takes long time on debug builds, here in particular:
http://buildbot.askmonty.org/buildbot/builders/p8-trusty-bintar-debug/builds/1027/steps/test/logs/stdio
and times out often. It might make sense to disable it for debug builds, or to reduce it somehow.

commit c395aad668bdf675b1a35f093c9f1d8d8570b7c4
Author: Jan Lindström <jan.lindstrom@mariadb.com>
Date: Thu Mar 31 13:12:48 2016 +0300

MDEV-9840: Test encryption.innodb-log-encrypt-crash fails on buildbot

Problem: We created more than 5 encryption keys for redo-logs.
Idea was that we do not anymore create more than one encryption
key for redo-logs but if existing checkpoint from earlier
MariaDB contains more keys, we should read all of them.

Fix: Add new encryption key to memory structure only if there
currently has none or if we are reading checkpoint from the log.
Checkpoint from older MariaDB version could contain more than
one key.