RFE: add --resource argument for cleaning up specific type of resources

[bregman-arie]

The usage would be: shade_janitor --cloud my_cloud --resource [network, router, subnet, instance,etc]
if for example user specified --resource network, it will delete all networks in a specific project.

This is useful in case you reached the quota limit for specific type of resources or you want to make sure no resource of type X exist in your tenant.

[yazug]

how would this work? since most of the resource cleanups are dependent on their parent being cleaned up first.

using current features you could run
shade_janitor/janitor.py --dryrun > cmds.txt
grep 'network' cmds.txt
and run those cleanup commands it would get any of the resources cleaned up that don't have other dependencies.