Create a `avocado plugins show` option

[beraldoleal]

As part of the Avocado 2020 vision, we could have a new command to display more detailed information about a plugin.

For instance:

$ avocado plugins show foo

This is related to #3476

[dkarpelevich]

@beraldoleal , What is the difference should be between the $ avocado plugins show vmimage and $ avocado vmimage -h? And if it's not CLICmd plugin the only information that can be shown is thedescription attribute.

[beraldoleal]

@dkarpelevich If you look to the output of avocado plugins | grep tap you will notice that for instance tap plugin has in a few sections: cli, results_events and resolver. The idea here is to improve this output to show that.

But also, this is just a not so discussed idea that we had during our Avocado Summit and AFAIK we are still doing changes here. So I would say that for now, this has a low priority.