KVM: selftests: Avoid KVM_SET_CPUID2 after KVM_RUN in hyperv_features test

hyperv_features's sole purpose is to test access to various Hyper-V MSRs
and hypercalls with different CPUID data. As KVM_SET_CPUID2 after KVM_RUN
is deprecated and soon-to-be forbidden, avoid it by re-creating test VM
for each sub-test.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20211122175818.608220-2-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>