Allow sharing of firewall rules and policies in policy.json

Updated policy for firewall_policy and firewall_rule to allow sharing
among tenants. Added a new firewall sharing rule to enable this.

Change-Id: I5d4d9f94fb3abffe4d1b03c46fd5b13a8a4a4f09
Fixes: bug #1217103
Merge "Allow sharing of firewall rules and policies in policy.json"