[all] extra requirement does not install all extras

PBR documentations states at https://docs.openstack.org/developer/pbr/#extra-requirements that is follows PEP-426 from https://www.python.org/dev/peps/pep-0426/#extras-optional-dependencies

Still, it seems that the implementation is incomplete as I was able to spot at least two bugs:

* Special "all" does not install all defines extras
* Special "alldev" extra does not install: test , build , doc , and dev extras.
* The documentation example is using "testing" extra name but the pep specifies "test" as the name. Use of standard names should be encouraged.

How to replicate? Edit setup.cfg and add one extras like:
```
[extras]
zzzz =
    aaaaaa
test =
    bbbbbb
```

Now you can test the behaviour by running commands like:
```
pip install -e '.[all]'
# supposed to pick both zzzz and test extras

pip install -e '.[alldev]'
# supposed to include test extra but it does not

pip install -e '.[zzzz]'
# this is the only one that works correctly
```

Note: you are free not skip using `-e` param because it does not change the behaviour.

Why is this bug so important? Is this bug would be solved we could all use the `pip install -e '.[all]'` as replacement for a full install that includes testing, a general interface that would work for any package even if they have test-requirements.txt files or not. This would be a great simplification.