Allow running standalone tests

Currently if i have standalone test generated, i can't find a good way to execute it.

What I do is:

Firstly, install **azdev**

pip install azdev

then setup your test environment:

azdev setup -c pypi

Login:

az login

and then i have to add test manually by:

vi ~/.azdev/env_config/env/test_index/latest.json

and adding:

{
"mytest": "/_/test_..... your test name.......py"
}

then running test:

azdev test mytest

I want to be able to just execute it directly:

azdev test /_/test_..... your test name.......py

This should be pretty simple change in azdev.