Add sample VNF coordinate script for rolling update with external components

This blueprint aims at supporting the rolling update with external management systems (e.g. OSS/EM).
Tacker has supported rolling updates by the ChangeCurrentVNFPackage API. However, the current Tacker does not have an explicit function to link with external management systems. Some rolling update scenarios require coordination with external components (e.g., changing load balancer settings from external components for authorization reasons.). VNF LCM Coordination interface defined in ETSI NFV SOL002 v3.5.1 [1] should be used for such scenarios.
This blueprint proposes implementing the client function of Coordination API in the Coordinate VNF script [2], which can be customized by the user without affecting the existing implementation.

[1] https://www.etsi.org/deliver/etsi_gs/NFV-SOL/001_099/002/03.05.01_60/gs_NFV-SOL002v030501p.pdf
[2] https://specs.openstack.org/openstack/tacker-specs/specs/yoga/upgrade-vnf-package.html