Fix v3 hypervisor extension servers action follow REST principles

The orignial hypervisor servers action as below:
'/os-hypervisors/[filters]/servers'

Change it as:
'/os-hypervisors/[hypervisor id]/servers'
And tt will return all the servers on the specific hypervisor.

Partially implements: bp v3-api-extension-versioning

DocImpact

Change-Id: I6c252372af67eda79f670199deb6592c02603c33
Merge "Fix v3 hypervisor extension servers action follow REST principles"