test_miniswift: add tests for SwiftClient.auth()
test_miniswift: add tests for SwiftClient.auth()

This brings `miniswift` test coverage to about 69%. It's not great, but
it's an improvement.

zerovm/zerovm-cli,zerovm/zpm,zerovm/zerovm-cli,zerovm/zpm,zerovm/zpm,zerovm/zerovm-cli,zerovm/zpm,zerovm/zpm,zerovm/zerovm-cli,zerovm/zerovm-cli,zerovm/zerovm-cli,zerovm/zpm