Use Tempest-lib's compute limits_client

Compute limits_client has been migrated to
tempest-lib- I80c6e148ae30148e591d24675fe068c829a0867a

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 limits_client
from Tempest-lib.

Change-Id: I915deafd6e513f98e4d621d4e91409dd35d6e19e
4 files changed