Set HOSTNAME to prevent tox 3.17+ from a DNS query

Tox calls socket.getfqdn() and that call does a DNS query.
In mock with disabled networking, it takes a minute until that times out.
When a spec file uses %pyproject_buildrequires -t and %tox, it is a 3 minute delay.

Since 3.17, tox does not call socket.getfqdn() when HOSTNAME variable is set to a value:

https://github.com/tox-dev/tox/pull/1616

The value is only used in result log, so setting it to "rpmbuild"
actually makes the logs more reproducible as well.

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1856356
when tox is used in %pyproject_buildrequires -t or %tox.

macros.pyproject

@@ -61,7 +61,7 @@ echo 'python3dist(toml)'
 # setuptools assumes no pre-existing dist-info
 rm -rfv *.dist-info/ >&2
 if [ -f %{__python3} ]; then
-  RPM_TOXENV="%{toxenv}" %{__python3} -I %{_rpmconfigdir}/redhat/pyproject_buildrequires.py %{?**}
+  RPM_TOXENV="%{toxenv}" HOSTNAME="rpmbuild" %{__python3} -I %{_rpmconfigdir}/redhat/pyproject_buildrequires.py %{?**}
 fi
 }
 
@@ -70,5 +70,6 @@ fi
 TOX_TESTENV_PASSENV="${TOX_TESTENV_PASSENV:-*}" \\
 PATH="%{buildroot}%{_bindir}:$PATH" \\
 PYTHONPATH="${PYTHONPATH:-%{buildroot}%{python3_sitearch}:%{buildroot}%{python3_sitelib}}" \\
+HOSTNAME="rpmbuild" \\
 tox --current-env -q --recreate -e "%{-e:%{-e*}}%{!-e:%{toxenv}}" %{?*}
 }

pyproject-rpm-macros.spec

@@ -6,7 +6,7 @@ License:        MIT
 
 # Keep the version at zero and increment only release
 Version:        0
-Release:        16%{?dist}
+Release:        17%{?dist}
 
 # Macro files
 Source001:      macros.pyproject
@@ -87,6 +87,7 @@ install -m 644 pyproject_save_files.py  %{buildroot}%{_rpmconfigdir}/redhat/
 
 %if %{with tests}
 %check
+export HOSTNAME="rpmbuild"  # to speedup tox in network-less mock, see rhbz#1856356
 %{python3} -m pytest -vv --doctest-modules
 %endif
 
@@ -100,6 +101,10 @@ install -m 644 pyproject_save_files.py  %{buildroot}%{_rpmconfigdir}/redhat/
 %license LICENSE
 
 %changelog
+* Wed Jul 15 2020 Miro Hrončok <mhroncok@redhat.com> - 0-17
+- Set HOSTNAME to prevent tox 3.17+ from a DNS query
+- Fixes rhbz#1856356
+
 * Fri Jun 19 2020 Miro Hrončok <mhroncok@redhat.com> - 0-16
 - Switch from upstream deprecated pytoml to toml