qemu.tests:Add stress_kernel_complie test case.

Add stress test for multi vms with kernel compile running
inside vm.
1. boot up vms
every VM has 4G vmem, the total vmem of VMs' are
$overcommit times as host's mem.(default overcommit=1.5)
2) Launch kernel compile inside every guest.

Changes from v1:
 - modify the parameter "i" to "vmnum"
 - remove "raise error" when kernel compile failed, just return error
to avoid the long message cause virtlab crash
 - put kernel path to virtlab cfg files
 - change the test failed check to ping test, and judge if the guest
can be reach after kernel compile.

Signed-off-by: Golita Yue <gyue@redhat.com>
Acked-by: Yiqiao Pu <ypu@redhat.com>
Acked-by: Amos Kong <akong@redhat.com>

Bin folder has been removed and most file in it have been moved to
client folder.

Signed-off-by: Feng Yang <fyang@redhat.com>