Use grub entries to find Linux kernels

Use grub entries to find Linux kernels

This change adds grub parsing to Lib.pm. It adds the following structure to $os:
  {boot}
  ->{configs}
    ->[0]
      ->{title}   = "Fedora (2.6.29.6-213.fc11.i686.PAE)"
      ->{kernel}  = \kernel
      ->{cmdline} = "ro root=/dev/mapper/vg_mbooth-lv_root rhgb"
      ->{initrd}  = \initrd
  ->{default} = 0

The kernel and initrd entries are just references to their top level entries
under kernels and initrd_modules respectively.

It also changes the way Linux kernels and initrd are discovered. Instead of
searching /lib/modules and /boot for files with matching names, kernels and
initrds are scanned as they are discovered in grub.conf.

Additionally, the following attributes are added to the kernels top level entry:
* path
    The path to the kernel's vmlinuz file.
* package
    The name of the package which installed the kernel.

The xml output of virt-inspector is updated to reflect all of the above changes.