Update heat policy.json
Update heat policy.json

This patch sets stacks:global_index to role:admin in /etc/heat/policy.json,
so that an admin role can look for all stacks in heat, which a magnum periodic
task will be benefited from it.

Partial-Implements: blueprint add-periodic-task
Change-Id: I4669ef355d302607f42df182bba680dc548e9618

Alzon/SUR,paulczar/magnum,Tennyson53/SUR,LaynePeng/magnum,paulczar/magnum,ffantast/magnum,Alzon/SUR,Tennyson53/SUR,ffantast/magnum,Tennyson53/magnum,ddepaoli3/magnum,openstack/magnum,ArchiFleKs/magnum,mjbrewer/testindex,openstack/magnum,dimtruck/magnum,mjbrewer/testindex,sajuptpm/magnum,hongbin/magnum,eshijia/SUR,dimtruck/magnum,jay-lau/magnum,ArchiFleKs/magnum,LaynePeng/magnum,annegentle/magnum,ramielrowe/magnum,hongbin/magnum,ddepaoli3/magnum,annegentle/magnum,ramielrowe/magnum,Tennyson53/magnum,mjbrewer/testindex,eshijia/SUR,eshijia/magnum,ChengTiesheng/magnum,eshijia/magnum,sajuptpm/magnum,ChengTiesheng/magnum