Updating to recent keystone/etc/policy.json.

Fixes bug 1185812.

Recent changes for validating tokens are required
as of https://review.openstack.org/#/c/23970/11

Without this change openstack services can't
validate token's and firstboot fails.

policy.json taken directly for the keystone repository.

Change-Id: I3efa6deb931e3b172fcb970aeb740576e10a86a9
Merge "Updating to recent keystone/etc/policy.json."