Description of problem:
while playing with dnf on centos7, after some update in libdnf, i noticed, that dnf related libraries and dnf itself are not updating, with message about unresolved dependencies. further investigation of libdnf spec revealed, that it has build requirement for swig >= 3.0.12, which is not in epel7/rhel7/centos7. and libdnf is dependency for librepo

Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
1. install dnf on centos7 from rpmsoftwaremanagement/dnf-nightly copr
2. run dnf clean metadata && dnf update
3. check output

Actual results:
Dependencies resolved.

 Problem: package python2-librepo-1.9.1-1.el7.x86_64 conflicts with python2-dnf < 2.8.8 provided by python2-dnf-2.8.5-0.101g0f20917d.el7.centos.noarch
  - cannot install the best update candidate for package python2-librepo-1.8.1-3gfd11033.el7.centos.x86_64
  - cannot install the best update candidate for package python2-dnf-2.8.5-0.101g0f20917d.el7.centos.noarch
============================================================================================================================================================================================================
 Package                                         Arch                                   Version                                     Repository                                                         Size
============================================================================================================================================================================================================
Skipping packages with conflicts:
(add '--best --allowerasing' to command line to force their upgrade):
 python2-librepo                                 x86_64                                 1.9.1-1.el7                                 rpmsoftwaremanagement-dnf-nightly                                  40 k

Transaction Summary
============================================================================================================================================================================================================
Skip  1 Package

Nothing to do.
Complete!
[root@shadow ~]# dnf update --best --allowerasing -C
Cache-only enabled but no cache for 'kraxel-flatpak', disabling.
Cache-only enabled but no cache for 'group_embedded-openocd', disabling.
Last metadata expiration check: 0:05:16 ago on Thu 30 Aug 2018 02:16:32 PM CEST.
Error: 
 Problem: The operation would result in removing the following protected packages: dnf
[root@shadow ~]# 

Expected results:
dnf and dependencies updated without problem

Additional info: