Add ServicePolicy and update PolicyLabels

New resource ServicePolicy is being added to model the resource that are
used for allocating resources (like IP addresses) that are used by the
service chain.

Also renaming PolicyLabels to PolicyTags and adding values attribute.

Change-Id: Ifa2d758a14f166a1b85be5ae5c1c6a075c9e0d3b
Merge "Add ServicePolicy and update PolicyLabels"