bug fix: add an icon distros list.

Now I create template with rhel iso, but when I create a VM from this
template, the template info displays differently with other templates.

That's because icon-rhel is missing for it is RED HAT trademark.

But this make us uncomfortable.
If the icon is missing we should display the default icon

Now there are only 7 icons, include the default icon icon-vm.

$ ls ui/images/*.png
ui/images/icon-centos.png  ui/images/icon-gentoo.png
ui/images/icon-debian.png  ui/images/icon-opensuse.png
ui/images/icon-fedora.png  ui/images/icon-ubuntu.png
ui/images/icon-vm.png

Signed-off-by: ShaoHe Feng <shaohef@linux.vnet.ibm.com>
pep8 clean for osinfo.py

pep8 clean for osinfo.py
add the file to PEP8_WHITELIST

Signed-off-by: ShaoHe Feng <shaohef@linux.vnet.ibm.com>