[FIX] Add pbr to requirements

[joao-p-marques]

The library is needed for the setup, but it is not specified in requirements.
Its installation depends on setuptools' easy_install, which is unreliable:

• https://docs.openstack.org/pbr/latest/#pbr-python-build-reasonableness
• https://pip.pypa.io/en/latest/cli/pip_install/#controlling-setup-requires

Example of the error that might be caused: https://github.com/Tecnativa/doodba/runs/2314862208?check_suite_focus=true#step:7:1476
Pre-installing pbr with pip solves the issue, so it could be added to the requirements.txt to force the installation that way.

ping @yajo

[yajo]

To reproduce easily:

docker container run --rm -it python:3.5-stretch bash -c 'python -m venv --system-site-packages /qa/venv && . /qa/venv/bin/activate && pip install pylint-odoo'

Result:

Collecting pylint-odoo
  Downloading https://files.pythonhosted.org/packages/74/ae/9cc3d387291e1e2866e0af906e1b76e766885867fe765a3f296f5879fd42/pylint-odoo-3.7.1.tar.gz (69kB)
    100% |████████████████████████████████| 71kB 3.2MB/s 
    Complete output from command python setup.py egg_info:
    Couldn't find index page for 'pbr' (maybe misspelled?)
    No local packages or working download links found for pbr
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-build-mrr8e_ga/pylint-odoo/setup.py", line 8, in <module>
        package_data={'': ['*.yaml']})
      File "/usr/local/lib/python3.5/distutils/core.py", line 108, in setup
        _setup_distribution = dist = klass(attrs)
      File "/qa/venv/lib/python3.5/site-packages/setuptools/dist.py", line 315, in __init__
        self.fetch_build_eggs(attrs['setup_requires'])
      File "/qa/venv/lib/python3.5/site-packages/setuptools/dist.py", line 361, in fetch_build_eggs
        replace_conflicting=True,
      File "/qa/venv/lib/python3.5/site-packages/pkg_resources/__init__.py", line 850, in resolve
        dist = best[req.key] = env.best_match(req, ws, installer)
      File "/qa/venv/lib/python3.5/site-packages/pkg_resources/__init__.py", line 1122, in best_match
        return self.obtain(req, installer)
      File "/qa/venv/lib/python3.5/site-packages/pkg_resources/__init__.py", line 1134, in obtain
        return installer(requirement)
      File "/qa/venv/lib/python3.5/site-packages/setuptools/dist.py", line 429, in fetch_build_egg
        return cmd.easy_install(req)
      File "/qa/venv/lib/python3.5/site-packages/setuptools/command/easy_install.py", line 659, in easy_install
        raise DistutilsError(msg)
    distutils.errors.DistutilsError: Could not find suitable distribution for Requirement.parse('pbr')
    
    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-mrr8e_ga/pylint-odoo/
You are using pip version 9.0.1, however version 21.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

However, this doesn't fix the problem. @joao-p-marques you probably need to patch something in setup.py and/or setup.cfg too. See:

╰─ docker container run --rm -it python:3.5-stretch bash -c 'python -m venv --system-site-packages /qa/venv && . /qa/venv/bin/activate && pip install git+https://github.com/Tecnativa/pylint-odoo.git@add-pbr-req'
Collecting git+https://github.com/Tecnativa/pylint-odoo.git@add-pbr-req
  Cloning https://github.com/Tecnativa/pylint-odoo.git (to add-pbr-req) to /tmp/pip-3sedwkrj-build
    Complete output from command python setup.py egg_info:
    Couldn't find index page for 'pbr' (maybe misspelled?)
    No local packages or working download links found for pbr
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-3sedwkrj-build/setup.py", line 8, in <module>
        package_data={'': ['*.yaml']})
      File "/usr/local/lib/python3.5/distutils/core.py", line 108, in setup
        _setup_distribution = dist = klass(attrs)
      File "/qa/venv/lib/python3.5/site-packages/setuptools/dist.py", line 315, in __init__
        self.fetch_build_eggs(attrs['setup_requires'])
      File "/qa/venv/lib/python3.5/site-packages/setuptools/dist.py", line 361, in fetch_build_eggs
        replace_conflicting=True,
      File "/qa/venv/lib/python3.5/site-packages/pkg_resources/__init__.py", line 850, in resolve
        dist = best[req.key] = env.best_match(req, ws, installer)
      File "/qa/venv/lib/python3.5/site-packages/pkg_resources/__init__.py", line 1122, in best_match
        return self.obtain(req, installer)
      File "/qa/venv/lib/python3.5/site-packages/pkg_resources/__init__.py", line 1134, in obtain
        return installer(requirement)
      File "/qa/venv/lib/python3.5/site-packages/setuptools/dist.py", line 429, in fetch_build_egg
        return cmd.easy_install(req)
      File "/qa/venv/lib/python3.5/site-packages/setuptools/command/easy_install.py", line 659, in easy_install
        raise DistutilsError(msg)
    distutils.errors.DistutilsError: Could not find suitable distribution for Requirement.parse('pbr')
    
    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-3sedwkrj-build/
You are using pip version 9.0.1, however version 21.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.