In our CI environment there is an artifical delay in between starting
the Rekor services via docker-compose and when the E2E tests are
actually executed due to Go modules being downloaded. In a local
development environment, the download may not be required so the tests
can start before the docker-compose services are actually running.

This introduces a healthcheck for services (where possible), and blocks
the start of the e2e tests until the services are reporting as healthy.
It also forces the use of an empty homedir and rekor config file to
ensure no collision between the tests and the developer's environment.

Fixes #183

Signed-off-by: Bob Callaway <bcallawa@redhat.com>