remove code duplication in tempest/config.py

tempest/config.py has many simliar tiny functions for register_*_opts.
We should remove the code duplication to providing a common function.

Change-Id: Ie8facc21a2d8a1e27687b1182a3db9f98bc1a05e
Closes-Bug: #1236498
Merge "remove code duplication in tempest/config.py"