Description of problem:
The mock postinstall scriptlet requires 'yum-utils' but does not Requires: it


Version-Release number of selected component (if applicable):
mock-1.4.2-1.fc26

How reproducible:
Every time

Steps to Reproduce:
1. Install a minimal install of Fedora (contains no python2 or yum-utils package)
2. `dnf install mock`

Actual results:
Post-install scriptlet fails (see below) and the configuration files are not properly generated.

Expected results:
Mock installs correctly.

Additional info:

  Running scriptlet: mock-1.4.2-1.fc26.noarch                                                      20/21 
/var/tmp/rpm-tmp.vovVtd: line 15: python: command not found
Warning: file /etc/mock/fedora-26-.cfg does not exists.
         unable to update /etc/mock/default.cfg

or after installing python (but not yum-utils):

  Running scriptlet: mock-1.4.2-1.fc26.noarch                                                      20/21 
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: No module named rpmUtils.arch
Warning: file /etc/mock/fedora-26-.cfg does not exists.
         unable to update /etc/mock/default.cfg