Correctly destoy RandomGenerator singleton
Correctly destoy RandomGenerator singleton

Change the implementation of Couchbase::RandomGenerator to be
correctly destoyed on process termination, removing the previous
memory leak (still reachable) which existed.

Note that C++11 guarantees that concurrent execution of the
initialization of the static member is thread-safe, so we can
significantly simplify the implementation by just using a static
member in the constructor.

Change-Id: Ifc169112d0d1fc870319df6bffb4eb301c38594f
Reviewed-on: http://review.couchbase.org/52778
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Jim Walker <1cd02e31b43620d7c664e038ca42a060d61727b9@couchbase.com>
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>

vmx/platform,vmx/platform