With this change the integration tests can now also be run as unit tests
against the mocked server. The way it works is this:
internal/client/unit_test.go sets up the mock server and is built
when the `integration` build tag is *not* included.
internal/client/integration_test.go sets up the connection to an
existing server and is built when the `integration` build tag *is*
included.
The test code is built and run for both cases.
Currently they all pass for the integration test run. The unit test
cases need some work because the mocked server isn't a real server with
real depsolving and package lists. A future commit will fix this.
856eb59edf