In order to adopt ginkgo incrementally, let's start by replacing
test/e2e/driver.go with a call to ginkgo runner and convert each of the
other tests to a small Decscribe() snippet that simply calls the legacy
TestXYZ function.

From this basis we can take further incremental steps by converting
individual tests to native ginkgo format, using Fail() for all failure
cases, using By() for logs, enabling JUnit reports, etc.

Tested:
- cmd/e2e builds and `make check` passes.
- Running _output/bin/.../e2e on an alive cluster works.
- Running the full hack/e2e-test.sh works as expected.