Description of problem:
When you run Mock (from epel-testing) on EL7 you get this traceback

 
mock -r epel-7-x86_64  --no-clean ./clamav-0.102.2-1.fc32.src.rpm 
....
Wrote: /builddir/build/SRPMS/clamav-0.102.2-1.el7.src.rpm
Traceback (most recent call last):
  File "/usr/bin/dnf", line 57, in <module>
    from dnf.cli import main
  File "/usr/lib/python2.7/site-packages/dnf/__init__.py", line 30, in
<module>
    import dnf.base
  File "/usr/lib/python2.7/site-packages/dnf/base.py", line 29, in
<module>
    import libdnf.transaction
  File "/usr/lib64/python2.7/site-packages/libdnf/__init__.py", line 3,
in <module>
    from . import conf
  File "/usr/lib64/python2.7/site-packages/libdnf/conf.py", line 17, in
<module>
    _conf = swig_import_helper()
  File "/usr/lib64/python2.7/site-packages/libdnf/conf.py", line 16, in
swig_import_helper
    return importlib.import_module('_conf')
  File "/usr/lib64/python2.7/importlib/__init__.py", line 37, in
import_module
    __import__(name)
ImportError: No module named _conf