virt: Make an example for set up params based on the kernel version

This is an example for set up params based on kernel version defined
in a cfg file named host-kernel.cfg. The main function for package
check(package_check) is in the control.kernel-version. Take
this as an example as kernel is a very important part in kvm test
and will decide a set of common parameters using in the cases. You
can also setup yourself host-package.cfg for different type of tests
in the same way.

changes from v1:
  - fix the typo for host_kernel_version_str
  - add one parameter for whether print out the debug messages
changes from v2:
  - typo fix

Signed-off-by: Yiqiao Pu <ypu@redhat.com>