Branch does not pass `isDevelopmentMode` check because it does not have
a version ending with `-next`. Therefore, `env.PWTEST_DOCKER_BASE_IMAGE`
is ignored which leads to the pull of non-existent image.
This patch introduces hidden commands to control container
lifecycle:
- `npx playwright docker install-server-deps` to install fluxbox,
vnc, novnc & to configure them.
- `npx playwright docker run-server` to run a server inside the
container.
Drive-by: remove old version of container image when building a new
version with the same name. This way we won't pile up untagged
container images.
