Fix typo in policy.json.sample
Fix typo in policy.json.sample

This patch fixes a type in policy.json.sample file.
Change role:is_admin to rule:is_admin

Change-Id: Ie2429fa8f73c2423fd396a54e2af86ef880f7dd4

openstack/ironic,openstack/ironic,NaohiroTamura/ironic,SauloAislan/ironic,pshchelo/ironic,SauloAislan/ironic,NaohiroTamura/ironic,pshchelo/ironic