Fix localtime handling for Xen-PV domains

At least Xen-3.4.3 translates the /vm/localtime SXPR value to
/domain/platform/localtime and /domain/image/{linux,hvm}/localtime when
the domain is defined.  When reading back that information libvirt only
handles HVM domains, but not PV domains: This results in libvirtd always
returning
    <clock offset="utc"/>
while Xend used (localtime 1).

For PV domains use /domain/image/linux/localtime.

src/xenxs/xen_sxpr.c

@@ -1195,6 +1195,9 @@ xenParseSxpr(const struct sexpr *root,
             def->clock.ntimers = 1;
             def->clock.timers[0] = timer;
         }
+    } else { /* !hvm */
+        if (sexpr_int(root, "domain/image/linux/localtime"))
+            def->clock.offset = VIR_DOMAIN_CLOCK_OFFSET_LOCALTIME;
     }
 
     /* Current XenD allows localtime here, for PV and HVM */