Mock fails with the ERROR below when the mock config directory doesn't contain a site-defaults.cfg file.  The tool does, however, succeed when the file exists but is empty.  Requiring that an empty file exist unnecessarily complicates Mock setup and makes it harder to use than it needs to be.  The command should treat a missing site-defaults.cfg the same as an empty file.

The following steps show the Mock failure and the steps required to make it work with a non-default config directory.  (Copying the logging.ini file is also inconvenient.  It would make it easier if Mock fell back to the same or some other reasonable defaults when the logging.ini file didn't exist.)

$ (dir=$PWD/mock-config; mkdir -p $dir && cp /etc/mock/logging.ini $dir/logging.ini && rhpkg mock-config > $dir/$(basename $PWD).cfg)
...
$ mock --configdir=$PWD/mock-config --no-cleanup-after -r patchutils --resultdir mock-results --rebuild $(rhpkg srpm | sed -n "s/^ *Wrote: *\(.*\)/\1/p")
ERROR: Could not find required config file: /home/msebor/rhel/patchutils/mock-config/site-defaults.cfg
ERROR:   If you're trying to specify a path, include the .cfg extension, e.g. -r ./target.cfg
...
$ : > mock-config/site-defaults.cfgpatchutils$ mock --configdir=$PWD/mock-config --no-cleanup-after -r patchutils --resultdir mock-results --rebuild $(rhpkg srpm | sed -n "s/^ *Wrote: *\(.*\)/\1/p")
INFO: mock.py version 1.2.4 starting (python version = 2.7.8)...
INFO: Start: init plugins
INFO: selinux enabled
INFO: Finish: init plugins
INFO: Start: run
INFO: Start(/home/msebor/rhel/patchutils/patchutils-0.3.3-4.el7.src.rpm)  Config(rhel-7.1-candidate-x86_64)
INFO: Start: clean chroot
...