azdev test -x, --exitfirst exit instantly on first error or failed test.

pytest has a parameter
```
-x, --exitfirst exit instantly on first error or failed test.
```
while azdev test has a opposite parameter
```
--no-exitfirst : Do not exit on first error or failed test.
```
pytest is the underlying tool of azdev.
I suggest keep the same with pytest. And `--no-exitfirst` breaks the original behavior.