Description of problem:

Get an error when running group operations as non root

Version-Release number of selected component (if applicable):
0.4.18

How reproducible:
everytime

Steps to Reproduce:
1. dnf group list
2.
3.

Actual results:
Traceback (most recent call last):
  File "/usr/bin/dnf", line 35, in <module>
    main.user_main(sys.argv[1:], exit_code=True)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 242, in user_main
    errcode = main(args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 74, in main
    return 1
  File "/usr/lib/python2.7/site-packages/dnf/base.py", line 116, in __exit__
    self.close()
  File "/usr/lib/python2.7/site-packages/dnf/base.py", line 245, in close
    self._store_persistent_data()
  File "/usr/lib/python2.7/site-packages/dnf/base.py", line 171, in _store_persistent_data
    self._group_persistor.save()
  File "/usr/lib/python2.7/site-packages/dnf/persistor.py", line 55, in save
    with open(self.db, 'w') as db:
IOError: [Errno 13] Permission denied: '/var/lib/dnf/groups.json'

Expected results:
No traceback

Additional info: