setup.py install misses some files if used with "--skip-build"

Hello,

I am packaging Gajim for Fedora. The Fedora packaging guidelines for Python (https://fedoraproject.org/wiki/Packaging:Python) suggest using a two-step process. There are predefined RPM macros called %py3_build and %py3_install. See "Steps to reproduce" where I expand the main parts of the macros. The problem is several directories are missing in the installed tree when the installation is performed in these two steps.

Versions

OS: Fedora 27
Gajim version: 1.0.0
GTK version: gtk3-3.22.26-2.fc27.x86_64
Python-nbxmpp version: 0.6.4

Steps to reproduce the problem

python3 setup.py build
python3 setup.py install --skip-build --root /tmp/gajim-bad

Expected behavior

All the expected files should be installed.

Actual behavior

The resulting tree is missing the following data directories: /usr/local/share/{metainfo,applications,man,locale}

When "--skip-build" is not used, all files are installed as expected.