kvm-unit-test: nSVM: Test SVME.EFER on VMRUN of nested guests

According to the section "Canonicalization and Consistency Checks" in 15.5.1
in APM vol 2, setting EFER.SVME to zero is an illegal guest state and will
cause the nested guest to VMEXIT to the guest with an exit code of
VMEXIT_INVALID.

Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>