KVM: selftests: Add "zero" testcase to set_memory_region_test

Add a testcase for running a guest with no memslots to the memory region
test.  The expected result on x86_64 is that the guest will trigger an
internal KVM error due to the initial code fetch encountering a
non-existent memslot and resulting in an emulation failure.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200410231707.7128-9-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>