Automatic update for mock-2.6-1.eln103.

Changelog

* Tue Sep 15 2020 Pavel Raiskup <praiskup@redhat.com> 2.6-1
- the --recurse option implies --continue
- fix --chain --continue option
- fail when --continue/--recurse is used without --chain
- fix _copy_config() for broken symlinks in dst= (rhbz#1878924)
- auto-download the source RPMs from web with --rebuild
- handle exceptions from command_parse() method
- fail verbosely for --chain & --resultdir combination
- allow using -a|--addrepo with /absolute/path/argument
- add support for -a/--addrepo in normal --rebuild mode
- use systemd-nspawn --resolv-conf=off
- create /etc/localtime as symlink even with isolation=simple (msuchy@redhat.com)
- dump the reason for particular package build fail in --chain
- raise PkgError when the source RPM can not be installed
* Thu Sep  3 2020 Pavel Raiskup <praiskup@redhat.com> 2.5-2
- because of the mock-filesystem change, we need to enforce upgrade
  of the old mock-core-configs package
* Thu Sep  3 2020 Pavel Raiskup <praiskup@redhat.com> 2.5-1
- set the DNF user_agent in dnf.conf (msuchy@redhat.com)
- introduce mock-filesystem subpackage (msuchy@redhat.com)
- add showrc plugin to record the output of rpm --showrc (riehecky@fnal.gov)
- document which packages we need in buildroot (msuchy@redhat.com)
- macros without leading '%' like config_opts['macros']['macroname'] work
  fine again (issue#605)