virttest.virt_vm: Update panic_re used in verify_kernel_crash

VMDeadKernelCrashError will be raised for following warning
call trace. This patch try to fix this issue.

------------[ cut here ]------------
[ 0.023009] WARNING: at arch/x86/kernel/cpu/amd.c:27 init_amd+0x10e/0x654()
[ 0.024004] Hardware name: KVM
[ 0.025004] rdmsrl_amd_safe should only be used on K8!
[ 0.026004] Modules linked in:
[ 0.028005] Pid: 0, comm: swapper/0 Not tainted 3.9.0-0.55.el7.x86_64 #1
[ 0.029004] Call Trace:
[ 0.030008] [] ? init_amd+0x10e/0x654
[ 0.031008] [] warn_slowpath_common+0x70/0xa0
[ 0.032006] [] warn_slowpath_fmt+0x4c/0x50
[ 0.033006] [] ? early_init_amd+0xb7/0xcd
[ 0.034008] [] init_amd+0x10e/0x654
[ 0.035006] [] identify_cpu+0x22c/0x357
[ 0.036010] [] identify_boot_cpu+0x10/0x3b
[ 0.037006] [] check_bugs+0x9/0x2d
[ 0.038007] [] start_kernel+0x3d1/0x409
[ 0.039006] [] ? repair_env_string+0x5c/0x5c
[ 0.040006] [] ? early_idt_handlers+0x120/0x120
[ 0.041006] [] x86_64_start_reservations+0x2a/0x2c
[ 0.042008] [] x86_64_start_kernel+0xf3/0x100
[ 0.043013] ---[ end trace d793b5b0c6ba38cc ]---

Changes in V2:
raise error.TestWarn for this kind warning call trace.

Signed-off-by: Feng Yang <fyang@redhat.com>