Fix 'make check' after commit 04197350

I broke 'make check' with commit 04197350 by unconditionally
emitting 'hap=' in xen xm driver.  Only emit 'hap=' if
xendConfigVersion >= 3.  I've tested sending 'hap=' to a Xen 3.2
machine without support for hap setting and verified that xend
silently drops the unrecognized setting.

src/xen/xm_internal.c

@@ -2413,6 +2413,7 @@ virConfPtr xenXMDomainConfigFormat(virConnectPtr conn,
                                (1 << VIR_DOMAIN_FEATURE_APIC)) ? 1 : 0) < 0)
             goto no_memory;
 
+        if (priv->xendConfigVersion >= 3)
             if (xenXMConfigSetInt(conf, "hap",
                                   (def->features &
                                    (1 << VIR_DOMAIN_FEATURE_HAP)) ? 1 : 0) < 0)