Add config for visibility of cisco-policy-profile

This change adds a configuration option to cisco_plugin.ini to control the
visibility of cisco-policy-profile among tenants. The default is false or
unrestricted, so all tenants can view all policy profiles. If the option
is set to true, tenants can only view policy profiles that are assigned
to that tenant. The admin user can always view all policy profiles. This
was implemented by adding a check of the configuration option in
get_policy_profiles().

Change-Id: I5d77544d75366d39714def971eb949cfdc40023e
Implements: blueprint cisco-policy-profile-visibility
Adding support of DNS nameserver and Host routes for the Nuage Plugin

This commit will implement the following DHCP options:
 - DNS nameserver
 - Host routes

Implements: blueprint dhcp-host-routes-and-dns-support-for-nuage-plugin
Change-Id: Idbb04f46112cddd588cad88921210aa0f63645f6
Make DhcpRpcCallback a separate callback class

RPC has a version of itself. In Neutron a plugin implements
several RPC interface, so a single RPC version doesn't work.
In Mixin callback class approach, RPC versioning depends on
each plugin implementation and it makes harder to maintain
RPC version appropriately. This patch series replaces mixin
RPC callback of server side with a separate class.

This commit handles server-side callback of dhcp-agent RPC interface.
DHCP-agent server-side callback class is moved from db/ to
api/rpc/handlers because it doesn't involve any db operations
and defining all RPC interfaces in a single place sounds reasonable.

Note that moving other DHCP-agent related RPC interface class
to api/rpc/handlers can be done in a separate patch as this patch
focuses on reorganizing the server-side RPC callback class.

Partial-Bug: #1359416
Change-Id: Ifb2a1bc0b7971995aae2856c9d4cd88c6dbc22d6
Merge "Adding support of DNS nameserver and Host routes for the Nuage Plugin"
Merge "Make DhcpRpcCallback a separate callback class"
Merge "Add config for visibility of cisco-policy-profile"