Remove unused method basic_auth from rest client

This method is not being used. Removing to reduce the area we need to cover in
the unit tests.

Related to bp unit-tests

Change-Id: I4ede8975d6fbbd4e5a4366f1ae2d771ffa526f91
Use BaseComputeTest.create_test_server

By using this instead of ClientServers.create_server, we inherit
everything that is automatically setup in
BaseComputeTest.create_test_server.

Change-Id: I4b6cbf8243083cb377323a4aff8de305d5c300f9
Merge "Remove unused method basic_auth from rest client"
Merge "Use BaseComputeTest.create_test_server"