Signed-off-by: NYumei Huang <yuhuang@redhat.com>

In case overcommit_host_mem, overcommit_mem need not exceed maxmem,
otherwise, keywords won't match. Fix it by set maxmem to a large
value.
Signed-off-by: NYumei Huang <yuhuang@redhat.com>

6 new cases to test hotplug mem negative options:
1.hotplug memory whose size overcommit host memory size
2.hotplug Min memory size=0
3.add memory device with no wrong numa node id
4.add memory backend with wrong size
5.memory backend ram option negtive test
6.memory device addr option negtive test
Signed-off-by: NZhenyu Zhang <zhenyzha@redhat.com>