copr: convert key to unicode before guessing lenght

addressing:
Traceback (most recent call last):
  File "/usr/bin/dnf", line 36, in <module>
    main.user_main(sys.argv[1:], exit_code=True)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 200, in user_main
    errcode = main(args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 83, in main
    return _main(base, args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 133, in _main
    cli.run()
  File "/usr/lib/python2.7/site-packages/dnf/cli/cli.py", line 1171, in run
    return self.command.run(self.base.extcmds)
  File "/usr/lib/python2.7/site-packages/dnf-plugins/copr.py", line 138, in run
    msg = self.base.output.fmtKeyValFill(msg, desc)
  File "/usr/lib/python2.7/site-packages/dnf/cli/output.py", line 704, in fmtKeyValFill
    keylen = exact_width(key)
  File "/usr/lib/python2.7/site-packages/dnf/i18n.py", line 164, in exact_width
    return sum(_exact_width_char(c) for c in msg)
  File "/usr/lib/python2.7/site-packages/dnf/i18n.py", line 164, in <genexpr>
    return sum(_exact_width_char(c) for c in msg)
  File "/usr/lib/python2.7/site-packages/dnf/i18n.py", line 138, in _exact_width_char
    return 2 if unicodedata.east_asian_width(uchar) in ('W', 'F', 'A') else 1
TypeError: must be unicode, not str