KVM: selftests: Update x86's KVM PV test to match KVM's disabling exits behavior

KVM: selftests: Update x86's KVM PV test to match KVM's disabling exits behavior

Rework x86's KVM PV features test to align with KVM's new, fixed behavior
of not allowing userspace to disable HLT-exiting after vCPUs have been
created.  Rework the core testcase to disable HLT-exiting before creating
a vCPU, and opportunistically modify keep the paired VM+vCPU creation to
verify that KVM rejects KVM_CAP_X86_DISABLE_EXITS as expected.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://lore.kernel.org/r/20241128013424.4096668-18-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>