go/zodb/zeo: Skip handshake/py/msgpack=true on ZEO4

ZEO4 does not have msgpack support and does not take $ZEO_MSGPACK into
account. With ZEO4 this test was failing before:

	--- FAIL: TestHandshake (0.46s)
	    --- FAIL: TestHandshake/py/msgpack=true (0.24s)
	        zeo_test.go:241: handshake: encoding=Z  ; want M

We don't have infrastructure to check python packages versions, so
check it by verifying ZEO.asyncio presence.

go/zodb/storage/zeo/zeo_test.go

@@ -192,6 +192,7 @@ func withZEOSrv(t *testing.T, f func(t *testing.T, zsrv ZEOSrv), optv ...tOption
 			needpy := []string{"ZEO"}
 			if msgpack {
 				needpy = append(needpy, "msgpack")
+				needpy = append(needpy, "ZEO.asyncio") // FIXME hack to check that ZEO ver >= 5
 			}
 			xtesting.NeedPy(t, needpy...)
 			withFS1(t, func(fs1path string) {