Added --direct_boot command line argument

When --direct_boot is specified, NIB assumes that nova is able to
interpret the kernel command line by reading the 'os_command_line'
property of a glance image.
The patch I applied earlier was not complete.
The patch I applied earlier was not complete.
Added needed changes to the Ubuntu plugin
Merge pull request #13 from redhat-imaging/feature/direct_boot

Feature/direct boot