MB-12067: Remove C++11 code from unit tests

Remove the C++11 code from the defragmenter unit tests so they will
build on pre-C++11 environments (e.g. CentOS 6).

Change-Id: I98e31eb8c9e95e82a0ce4f67dab2d1c9c2064993
Reviewed-on: http://review.couchbase.org/44108
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Dave Rigby <daver@couchbase.com>
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>