pybind/mgr: install setuptools >= 12

pybind/mgr: install setuptools >= 12

otherwise we have
```
  Running setup.py egg_info for package apache-libcloud

    libcloud/utils/py3.py:76: UserWarning: Missing backports.ssl_match_hostname package
      warnings.warn("Missing backports.ssl_match_hostname package")
    Traceback (most recent call last):
...
      File "build/bdist.linux-x86_64/egg/setuptools_scm/version.py", line 66, in _warn_if_setuptools_outdated

...
setuptools_scm.version.SetuptoolsOutdatedWarning: your setuptools is too old (<12)
...
Command python setup.py egg_info failed with error code 1 in /tmp/tmp.i95Fg82Ea4/venv/build/apache-libcloud
```

and more important thing is, setuptools >= 12 allows us to install the
python modules in venv, without uninstalling existing modules if they
are also installed in by system packages.

Signed-off-by: Kefu Chai <kchai@redhat.com>