set per request one client for sync protection status

[yinwei]

During integrating hybrid-cloud with smaug, we found that cinder protection plugin uses a global cinder client (one client per protection plugin) to query protection status.
This will be a bug where there're parallel protection requests with multiple tenants.
We need save cinder client as per protection context, and use it to sync status in background.

[Saggi Mizrahi (ficoos)]

This is unrelated to hybrid cloud. We do need to support having multiple contexts.

[zengchen (chenzeng2)]

I think it is not still a bug, if the new protection service framework( http://review.openstack.org/#/c/348163) is merged. Because it will create a set of new individual protection plugin instances for each request(https://review.openstack.org/#/c/348163/24/karbor/services/protection/flows/create_protection.py #58 line). Then the other openstack service clients created in plugin will not be shared between two different requests.