Issue #48: grub.conf isn't correctly modified with kickstart script

- Use full path when running grubby
- Remove sed commands which disable hiddenmenu and splashimage options.
There is no need to add corresponding grubby commands to remove these options
because there is no splashimage to point at and no need to disable hiddenmenu
- Remove sed command which sets the title based on the loaded kernel.  This is
unnecessary because this title is included as a menuentry item automatically
with the name/kernel version set via the /etc/default/grub config file.