if two or more kernel packages are installed into $rootimg_dir/boot/,
the value of "<$rootimg_dir/boot/vmlinux-*>" will be one array, not a file,
which can lead to one error for the copy() subroutine in File::Copy.
git-svn-id: https://svn.code.sf.net/p/xcat/code/xcat-core/trunk@5835 8638fb3e-16cb-4fca-ae20-7b5d299a9bcd