This migrates the above files from tempest. This includes tempest commits:
* extensions_client.py : I8dcb70ce6ba2af59c7636c5f83157dd058fb1df3
* test_extensions_client.py: I3ad6761651cec5e66012d08e6b63322f53286a5c
* extensions.py : Ica929c402a3d042ae751302384e68853eb28b405
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: Ic658f09649ed9498fe6d3e7792a7c370772f165b