Relation building for host mapping attributes

[sushanthakumar]

Issue/Feature Description: Delfin host mapping feature involves collection of resources such as storage host initiators, storage hosts, storage host groups, volumes/volume groups, port/port groups . Apart from syncing these individual resources, the relation between group and items also need to be constructed and maintained. This involves hostgrp-host relation, volumegrp-volume relation and portgrp-port relation

Feature Design doc for reference: RequirementsDesignSpec_HostMapping.docx

Why this issue to fixed / feature is needed(give scenarios or use cases):

How to reproduce, in case of a bug:

Other Notes / Environment Information: (Please give the env information, log link or any useful information for this issue)

[joseph-v]

PR #793