Update subcommands to support loader filter

These changes update the subcommands to support a file/directory name
filter. This allows users to exclude certain files from being loaded.
With these changes users can excldue private directories created by
Kubernetes for volume-mounted ConfigMaps.

As part of this change, update the Kubernetes deployment documentation
to use the new --ignore flag, run OPA as a Deployment instead of as a
ReplicationController, and generally improve the example.

Fixes #782

Signed-off-by: Torin Sandall <torinsandall@gmail.com>