shared.unattended: Disable the color display from console

The default bashrc for root in Ubuntu will enable color display
in the console. This caused unreadable characters for some
cmd output, like 'ls'. It will fail our cases as script can not
get the output we want. So disable it in preseed files for install.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Merge pull request #1356 from ypu/ubuntu

shared.unattended: Disable the color display from console