Better support for nested directories - v2

[jasonish]

Rebase of https://github.com/OISF/suricata-verify/pull/1487.

First, if doing run.py pattern consider the directories to the test as part of the test name. For example you might have a directory foobar with tests named one, two and so on. You'd want run.py foobar to run all those tests.

Second, handle more then one level of sub-directories when displaying the test name.

[jufajardini]

This is most welcome! I think it would deserve a readme update.