Add a couple of test improvements triggered by changes in ubuntu:latest image.

- Relax getcap assertion to accept both old "path = caps+p" and new
  "path caps=p" formats (libcap output changed).
- Use uid 1001 for the unprivileged test user; uid 1000 is now the
  default "ubuntu" user in ubuntu:resolute and later.

Signed-off-by: Cesar Talledo <cesar.talledo@docker.com>