KVM: selftests: Convert vmx_apic_access_test away from VCPU_ID

Convert vmx_apic_access_test to use vm_create_with_one_vcpu() and pass
around a 'struct kvm_vcpu' object instead of using a global VCPU_ID.

Opportunistically make the "vm" variable local, it is unused outside of
main().

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>