setvcpus: Test maximum CPUs exceeding topology limit

Start guest will fail if maximum CPUs greater than topology limit.

Signed-off-by: Yanbing Du <ydu@redhat.com>
setvcpus: Clear test steps and add a new case

1. The original test hard code the maximum vcpu number to 2, and the
test steps are not clear and maintain, so re-organize the case to make
it more clear.

2. Add a case to test vcpu hotplug without <acpi> feature

Signed-off-by: Yanbing Du <ydu@redhat.com>
Merge pull request #304 from will-Do/setvcpus

setvcpus: Case update and add new cases