Add KVM modlue check logic

fixed #20
update module check logic

- adopt p0deje's suggestion
fix broken unless block
check return value of system("modprobe kvm")

Signed-off-by: Hiroshi Miura <miurahr@linux.com>
Merge pull request #67 from miurahr/check_kvm_kernel_module

Add KVM modlue check and loading kvm kernel module
close #20