Use Tempest-lib's compute hosts_client

Compute hosts_client has been migrated to
tempest-lib- I59c82bc896d5036d936e6f9cddb3c7b004648dde

Now Tempest-lib provides this client as stable interface so Tempest
should start using this from lib and remove its own copy.
Also remove its unit tests.

This commits makes Tempest to use compute hosts_client
from Tempest-lib.

Change-Id: I5f0846c3fbe2100223f01f9aa9b22c10d75a2468
4 files changed