With such a simple image it would be fairly trivial to paste it into photoshop, invert it and then select the (now) black backround and delete it leaving just the white line. Then you should be able to paste it into Keynote or safe it as a PNG or TIFF and inport it into Keynote. This is all speculatoin however as I don not own Photoshop, Illustrator or Keynote...
Wesley