Can not run image-creator command line on RPM based system

[Mitz Amano]

Bug detailed description:
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Can not run image-creator command line on RPM based system.

Reproduce steps:
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1.Open image-creator(Fedora 9).

Current result:
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% sudo image-creator --command=create-project --project-name='Sample'
Traceback (most recent call last):
  File "/usr/bin/image-creator", line 21, in <module>
    import gtk
  File "/usr/lib/python2.5/site-packages/gtk-2.0/gtk/__init__.py", line 79, in <module>
    _init()
  File "/usr/lib/python2.5/site-packages/gtk-2.0/gtk/__init__.py", line 67, in _init
    _gtk.init_check()
RuntimeError: could not open display

Could not create a live-rw-usb by command line.

Expected result:
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Can run image-creator command line.

Basic root-causing log:
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