avocado.plugins.collector: Collect results in JSON format and archive logs.

Collect and output test results in JSON format,
implies option to archive logs in ZIP format.

Signed-off-by: Ruda Moura <rmoura@redhat.com>
Merge pull request #68 from ruda/avocado_plugins_collector

avocado.plugins.collector: Collect results in JSON format and archive logs