Description of problem:

If I try to run gnome-abrt without abrt-dbus installed it fails with traceback and exists. 
However there is not dependency on abrt-dbus from gnome-abrt, so one can install currently broken configuration.

If it is expected to run gnome-abrt without abrt-dbus, it definitely shouldn't traceback but show some warning that there will be no connection to system abrt.
If there is no such expectation please set requires so gnome-abrt will work without explicit install of abrt-dbus.

Version-Release number of selected component (if applicable):
gnome-abrt-0.3.1-1.el7.x86_64

How reproducible:
always

Steps to Reproduce:
1. make sure there is no abrt-dbus installed
2. gnome-abrt


Actual results:
WARNING:root:Traceback (most recent call last):
  File "/usr/bin/gnome-abrt", line 212, in do_activate
    get_standard_problems_source(self._dbus_srv.mainloop))
  File "/usr/lib64/python2.7/site-packages/gnome_abrt/dbus_problems.py", line 38, in get_standard_problems_source
    return DBusProblemSource(StandardProblems, mainloop)
  File "/usr/lib64/python2.7/site-packages/gnome_abrt/dbus_problems.py", line 82, in __init__
    self._connect_to_problems_bus()
  File "/usr/lib64/python2.7/site-packages/gnome_abrt/dbus_problems.py", line 103, in _connect_to_problems_bus
    .format(BUS_NAME, BUS_PATH, ex))
UnavailableSource: Can't connect to DBus system bus 'org.freedesktop.problems' path '/org/freedesktop/problems': org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.problems was not provided by any .service files

ERROR:root:Can't connect to DBus system bus 'org.freedesktop.problems' path '/org/freedesktop/problems': org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.problems was not provided by any .service files
Traceback (most recent call last):
  File "/usr/bin/gnome-abrt", line 228, in do_activate
    (_("System"), get_foreign_problems_source())]
  File "/usr/lib64/python2.7/site-packages/gnome_abrt/dbus_problems.py", line 41, in get_foreign_problems_source
    return DBusProblemSource(ForeignProblems, mainloop)
  File "/usr/lib64/python2.7/site-packages/gnome_abrt/dbus_problems.py", line 82, in __init__
    self._connect_to_problems_bus()
  File "/usr/lib64/python2.7/site-packages/gnome_abrt/dbus_problems.py", line 103, in _connect_to_problems_bus
    .format(BUS_NAME, BUS_PATH, ex))
UnavailableSource: Can't connect to DBus system bus 'org.freedesktop.problems' path '/org/freedesktop/problems': org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.problems was not provided by any .service files

Expected results:
 no error - either by installed requires or being able to work without dbus connection 

Additional info: