Implement vim status update in conductor

[OpenStack Infra]

https://review.openstack.org/475594
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.
Your project "openstack/tacker" is set up so that we directly report the documentation bugs against it. If this needs changing, the docimpact-group option needs to be added for the project. You can ask the OpenStack infra team (#openstack-infra on freenode) for help if you need to.

commit 755a55ad5f98206166665a2bb88fe7ca25a144dc
Author: jing.liuqing <[e-mail]>
Date: Tue Jun 20 06:37:31 2017 +0800

    Implement vim status update in conductor

    Mistral vim monitor task connects to conductor via conductor's AMQP
    topic, calls the update_vim RPC method.

    The RPC method will update vim and event DB entries and then return
    passed in status.

    This patch refactors the common_services_db and nfvo_db in order
    not to import too many classes in the conductor process.

    One more thing is on devstack, where tacker-conductor service is
    introduced.

    DocImpact
    Implements: blueprint refactor-vim-monitor

    Change-Id: Ic2b3c381cca796edc00f3c77cc790cb4c4955db7