This migrates the above files from tempest.
This includes tempest commits:
* agents_client.py : I505fa196c574027692497848d235781d903cb9f6
* subnetpools_client.py: I405a896b4da0c5cb5bc87622d07498c06932f406
to see the commit history for these files refer to the above Change-Ids
in the tempest repository.
Partially implements blueprint migrate-service-clients-to-tempest-lib
Change-Id: I97b67e2385452db6ef59bc4b8c63c211ca119bc2