KVM: selftests: Convert state_test away from VCPU_ID

Convert state_test to use vm_create_with_one_vcpu() and
vm_recreate_with_one_vcpu(), and pass around a 'struct kvm_vcpu' object
instead of using a global VCPU_ID.  Note, this is a "functional" change
in the sense that the test now creates a vCPU with vcpu_id==0 instead of
vcpu_id==5.  The non-zero VCPU_ID was 100% arbitrary and added little to
no validation coverage.  If testing non-zero vCPU IDs is desirable for
generic tests, that can be done in the future by tweaking the VM creation
helpers.

Opportunistically use vcpu_run() instead of _vcpu_run(), the test expects
KVM_RUN to succeed.

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