Stop admin using other tenants unshared rules

If the firewall rules are not shared and if they belong to different
tenants, then admin should not be able to create a policy using
these rules and he should not be able to insert such rules into
policies. An exception should be raised in such case. Added new
exception “FirewallRuleConflict” to handle such conditions.

Co-Authored-By: Koteswara Rao Kelam<koteswara.kelam@hp.com>
Change-Id: I984eb76069bd1493a77bf523bec2bd81abb14abb
Closes-bug: 1327057
Merge "Stop admin using other tenants unshared rules"
Merge branch 'master' of https://github.com/openstack/quantum