Description of problem:
rhel6 only support the max is 160, but if boot guest with vcpus that is bigger than allowed, qemu will core dumped.
rhel7 support the max is 255, if boot guest with 256, qumu will quit automatically with some warning 'Unsupported number of maxcpus'.

Version-Release number of selected component (if applicable):
host info:
2.6.32-402.el6.x86_64
qemu-kvm-0.12.1.2-2.381.el6.x86_64
seabios-0.6.1.2-28.el6.x86_64
guest info:
2.6.32-402.el6.x86_64

How reproducible:
100%

Steps to Reproduce:
1.boot guest with vcpus that is bigger than allowed(160).
# /usr/libexec/qemu-kvm -S -M rhel6.5.0 -cpu SandyBridge -enable-kvm -m 4096 -smp 161 -no-kvm-pit-reinjection...
2.
3.

Actual results:
after step 1, qemu will core dumped.
kvm_create_vcpu: Invalid argument
Failed to create vCPU. Check the -smp parameter.
Aborted (core dumped)

Core was generated by `/usr/libexec/qemu-kvm -S -M rhel6.5.0 -cpu SandyBridge -enable-kvm -m 4096 -smp'.
Program terminated with signal 6, Aborted.
#0  0x00007f5fc5a558a5 in raise () from /lib64/libc.so.6
(gdb) bt
#0  0x00007f5fc5a558a5 in raise () from /lib64/libc.so.6
#1  0x00007f5fc5a57085 in abort () from /lib64/libc.so.6
#2  0x00007f5fc8142e5b in kvm_create_vcpu (_env=<value optimized out>) at /usr/src/debug/qemu-kvm-0.12.1.2/qemu-kvm.c:475
#3  ap_main_loop (_env=<value optimized out>) at /usr/src/debug/qemu-kvm-0.12.1.2/qemu-kvm.c:2026
#4  0x00007f5fc7a75851 in start_thread () from /lib64/libpthread.so.0
#5  0x00007f5fc5b0b90d in clone () from /lib64/libc.so.6
(gdb)

Expected results:
it should give a friendly prompt, like: nsupported number of maxcpus.

Additional info:
# /usr/libexec/qemu-kvm -S -M rhel6.5.0 -cpu SandyBridge -enable-kvm -m 4096 -smp 161 -no-kvm-pit-reinjection -name sluo -uuid 43425b70-86e5-4664-bf2c-3b76699a8aec -rtc base=localtime,clock=host,driftfix=slew -device virtio-serial-pci,id=virtio-serial0,max_ports=16,vectors=0,bus=pci.0,addr=0x3 -chardev socket,id=channel1,path=/tmp/helloworld1,server,nowait -device virtserialport,chardev=channel1,name=com.redhat.rhevm.vdsm.1,bus=virtio-serial0.0,id=port1,nr=1 -chardev socket,id=channel2,path=/tmp/helloworld2,server,nowait -device virtserialport,chardev=channel2,name=com.redhat.rhevm.vdsm.2,bus=virtio-serial0.0,id=port2,nr=2 -drive file=/dev/vg/system-disk.raw,if=none,id=drive-system-disk,format=raw,cache=none,aio=native,werror=stop,rerror=stop,serial="QEMU-DISK1" -device virtio-scsi-pci,bus=pci.0,addr=0x4,id=scsi0 -device scsi-hd,drive=drive-system-disk,id=system-disk,bootindex=1 -device virtio-balloon-pci,id=ballooning,bus=pci.0,addr=0x5 -global PIIX4_PM.disable_s3=0 -global PIIX4_PM.disable_s4=0 -netdev tap,id=hostnet0,vhost=off,script=/etc/qemu-ifup -device virtio-net-pci,netdev=hostnet0,id=virtio-net-pci0,mac=2C:41:38:B6:32:21,bus=pci.0,addr=0x6,bootindex=2 -drive file=/dev/vg/my-data-disk.raw,if=none,id=drive-data-disk,format=raw,media=disk,cache=none,aio=native,werror=stop,rerror=stop,serial="QEMU-DISK2" -device virtio-scsi-pci,bus=pci.0,addr=0x7,id=scsi1 -device scsi-hd,drive=drive-data-disk,id=data-disk,bootindex=3,bus=scsi1.0 -k en-us -boot menu=on -vnc :1 -spice port=5931,disable-ticketing -qmp tcp:0:4444,server,nowait -monitor stdio