ceph-volume: add "packaging" to install_requires

ceph-volume: add "packaging" to install_requires

in 0985e201, "packaging" was introduced as a runtime dependency of
ceph-volume, and `ceph.spec.in` was updated accordingly to note
this new dependency. but the debian packaging was not updated.

in 80edcd40, the missing dependency was added to debian/control as
one of ceph-volume's runtime dependency.

but dh_python3 is able to figure out the dependencies by reading
the egg's metadata of the ceph-volume python module. and as a
python project, ceph-volume is using its `setup.py` for
tracking its dependencies.

so in order to be more consistent, and keep all of its dependencies
in one place, let's move this dependency to setup.py . as the
packagings in both distros are able to figure the dependencies
from egg-info.

see also
- https://manpages.debian.org/testing/dh-python/dh_python3.1.en.html#dependencies
- https://docs.fedoraproject.org/en-US/packaging-guidelines/Python_201x/#_automatically_generated_dependencies

Signed-off-by: Kefu Chai <tchaikov@gmail.com>