Allow target selection in all namespaces

[royreznik]

Hi :)

I started to use mirrord lately, and i found something that could be really cool
We have like 10 namespaces in your product, and when i want to mirror one pod, i need to choose the namespace that Im currently working on, before using the mirrord plugin.

I thought that could be really nice to have an option to see all the pods from all namespaces.
This will be really nice, and probably useful for everyone

After quick look at the code it seems like the plugin use the mirrord ls, which at least for now doesn't have the feature, so i guess it will need to be implement there.

I think of something -A in kubectl