Raise exception/403 on attempt to reuse ip-address

[Hampapur Ajay]

Currently (3.0 and beyond) if an instance-ip object attempts to reserve an in-use address, it will not be set in instance_ip_address prop but no exception is returned back. Fix that and also add validations so that:

1. raise 403 on any attempt to reserve an ip already in use by instance-ip (except gw-ip)/floating-ip
2. for gw-ip address, allow only if vmi is not pointing to a vm. i.e. gateway-ip cannot be attracted by vm but it is ok to put it on a router-port

[OpenContrail Admin (ci-admin-f)]

Review in progress for https://review.opencontrail.org/17783
Submitter: Hampapur Ajay (<email address hidden>)

[OpenContrail Admin (ci-admin-f)]

Reviewed: https://review.opencontrail.org/17783
Committed: http://github.org/Juniper/contrail-controller/commit/fb9165b6f12e74a3103e1da7088969434ce956d8
Submitter: Zuul
Branch: master

commit fb9165b6f12e74a3103e1da7088969434ce956d8
Author: Hampapur Ajay <email address hidden>
Date: Tue Feb 23 14:51:19 2016 -0800

Disallow re-use of ip-address and add validations for iip, fip, vmi.
Refactor to put dbe_read and error handling in Resource class.

Partial-Bug: #1549572

Change-Id: I4838fac7f9d3d9f59d5e7fabb5578529b69e2901

[OpenContrail Admin (ci-admin-f)]

Review in progress for https://review.opencontrail.org/17875
Submitter: Hampapur Ajay (<email address hidden>)

[OpenContrail Admin (ci-admin-f)]

Reviewed: https://review.opencontrail.org/17875
Committed: http://github.org/Juniper/contrail-controller/commit/af4ac2ebfedcedd6cc01747140f432bbe4714562
Submitter: Zuul
Branch: R3.0

commit af4ac2ebfedcedd6cc01747140f432bbe4714562
Author: Hampapur Ajay <email address hidden>
Date: Tue Feb 23 14:51:19 2016 -0800

Disallow re-use of ip-address and add validations for iip, fip, vmi.
Refactor to put dbe_read and error handling in Resource class.

Partial-Bug: #1549572

Change-Id: I4838fac7f9d3d9f59d5e7fabb5578529b69e2901
(cherry picked from commit fb9165b6f12e74a3103e1da7088969434ce956d8)