host-kernel-check.cfg:Add RHEL.6.8 host kernel check

Signed-off-by: NYanan Fu <yfu@redhat.com>

qemu/cfg/host-kernel/host-kernel-check.cfg

@@ -61,6 +61,9 @@ variants:
                     - u7:
                         host_kernel_ver_str += ".7"
                         requires_kernel = [">= 2.6.32-505", "<  2.6.32-574"]
+                    - u8:
+                        host_kernel_ver_str += ".8"
+                        requires_kernel = [">= 2.6.32-574", "<  2.6.32-643"]
             - m7:
                 host_kernel_ver_str += ".7"
                 variants: