avocado.plugins.runner:  Export the test runner parser.

Export the test runner parser back to the main parser,
so you can use `parser.runner` to extend it.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
avocado.plugins: Move plugins to the runner.

Move plugins journal, json, xunit and vm inside the test runner
subcommand, now the command line options belongs to the runner,
instead of the main application.

Signed-off-by: Ruda Moura <rmoura@redhat.com>