MB-25521 Ensure phosphor is initialised before file_logger uses atexit
MB-25521 Ensure phosphor is initialised before file_logger uses atexit

While 615e410 ensured that the file_logger was explicitly shutdown
before memcached returns from main, it is still possible that during
an unclean shutdown caused by std::exit or breakpad that the file
logger thread could attempt to deregister from phosphor after
phosphor has deinitialised - resulting in a SEGV.

This doesn't cause any significant problems since the shutdown is
already unclean but can cause confusion as to what caused the unclean
exit.

Change-Id: I2600e56a13897d0088df8e5fcbae3f82b454efd7
Reviewed-on: http://review.couchbase.org/81894
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine