Assemble Xen NIC parameters into a dictionary

... instead of a string. This reduces the chance of programmer errors
and also eliminates the need to include comma separators everywhere.
Signed-off-by: Petr Pudlak <pudlak@google.com>
Reviewed-by: Helga Velroyen <helgav@google.com>

lib/hypervisor/hv_xen.py

@@ -588,29 +588,31 @@ class XenHypervisor(hv_base.BaseHypervisor):
           (nic_type, constants.HT_HVM_VIF_IOEMU)
 
     for idx, nic in enumerate(instance.nics):
-      nic_str = "mac=%s%s" % (nic.mac, nic_type_str)
+      nic_args = {}
+      nic_args["mac"] = "%s%s" % (nic.mac, nic_type_str)
 
       ip = getattr(nic, "ip", None)
       if ip is not None:
-        nic_str += ", ip=%s" % ip
+        nic_args["ip"] = ip
 
       if nic.nicparams[constants.NIC_MODE] == constants.NIC_MODE_BRIDGED:
-        nic_str += ", bridge=%s" % nic.nicparams[constants.NIC_LINK]
+        nic_args["bridge"] = nic.nicparams[constants.NIC_LINK]
       elif nic.nicparams[constants.NIC_MODE] == constants.NIC_MODE_OVS:
-        nic_str += ", bridge=%s" % nic.nicparams[constants.NIC_LINK]
+        nic_args["bridge"] = nic.nicparams[constants.NIC_LINK]
         if nic.nicparams[constants.NIC_VLAN]:
-          nic_str += "%s" % nic.nicparams[constants.NIC_VLAN]
+          nic_args["bridge"] += nic.nicparams[constants.NIC_VLAN]
 
       if nic.name and \
             nic.name.startswith(constants.INSTANCE_COMMUNICATION_NIC_PREFIX):
         tap = hv_base.GenerateTapName()
-        nic_str += ", vifname=%s" % tap
+        nic_args["vifname"] = tap
         nic.name = tap
 
       if hvp[constants.HV_VIF_SCRIPT]:
-        nic_str += ", script=%s" % hvp[constants.HV_VIF_SCRIPT]
+        nic_args["script"] = hvp[constants.HV_VIF_SCRIPT]
 
-      vif_data.append("'%s'" % nic_str)
+      nic_str = ", ".join(["%s=%s" % p for p in nic_args.items()])
+      vif_data.append("'%s'" % (nic_str, ))
       self._WriteNICInfoFile(instance, idx, nic)
 
     config.write("vif = [%s]\n" % ",".join(vif_data))