property: fix GIL deadlock on destruction

Change-Id: I4c666ad7410aa887bee48fb4d21b75057c631daa
Reviewed-on: http://gerrit.aldebaran.lan/50093
Reviewed-by: jlamotte <jlamotte@aldebaran.com>
Reviewed-by: pdaouadi <pdaouadi@aldebaran-robotics.com>
Tested-by: pdaouadi <pdaouadi@aldebaran-robotics.com>