Allow to specify a remote tftp server and pxe loader name

New keys for l2_network_device:

- pxe_bootp_file: filename of PXE loader, default='pxelinux.0'
- pxe_bootp_server: IP address of TFTP server that should be used
                    instead of the libvirt host. default=None

Change-Id: I5b15bcdb623638df939eddf78cf1ff90efa08a7f

devops/driver/libvirt/libvirt_driver.py

@@ -379,7 +379,9 @@ class LibvirtL2NetworkDevice(network.L2NetworkDevice):
                      #  than will be used 'stp' setting from the driver object.
 
        has_pxe_server: false  #  Enable PXE server for this device
-       tftp_root_dir: /tmp    #  Specity root directory for TFTP server
+       pxe_bootp_file: pxelinux.0  #  Name of the PXE loader file
+       tftp_root_dir: /tmp     #  Specify root directory for TFTP server, or
+       pxe_bootp_server: None  #  Specify IP address of the TFTP server
 
        vlan_ifaces: []  #  List of integer values that will be used to create
                         #  tagged interfaces to the network device.
@@ -527,6 +529,8 @@ class LibvirtL2NetworkDevice(network.L2NetworkDevice):
     stp = base.ParamField()
 
     has_pxe_server = base.ParamField(default=False)
+    pxe_bootp_file = base.ParamField(default='pxelinux.0')
+    pxe_bootp_server = base.ParamField()
     tftp_root_dir = base.ParamField()
 
     vlan_ifaces = base.ParamField(default=[])
@@ -648,6 +652,8 @@ class LibvirtL2NetworkDevice(network.L2NetworkDevice):
             has_pxe_server=self.has_pxe_server,
             dhcp=self.dhcp,
             tftp_root_dir=self.tftp_root_dir,
+            pxe_bootp_file=self.pxe_bootp_file,
+            pxe_bootp_server=self.pxe_bootp_server,
         )
         ret = self.driver.conn.networkDefineXML(xml)
         ret.setAutostart(True)

devops/driver/libvirt/libvirt_xml_builder.py

@@ -42,7 +42,8 @@ class LibvirtXMLBuilder(object):
                           ip_network_prefixlen=None, stp=True,
                           has_pxe_server=False, dhcp=False,
                           dhcp_range_start=None, dhcp_range_end=None,
-                          tftp_root_dir=None):
+                          tftp_root_dir=None, pxe_bootp_file='pxelinux.0',
+                          pxe_bootp_server=None):
         """Generate network XML
 
         :rtype : String
@@ -87,8 +88,11 @@ class LibvirtXMLBuilder(object):
                                 name=address['name'],
                             )
                         if has_pxe_server:
-                            network_xml.bootp(file='pxelinux.0')
-
+                            if pxe_bootp_server:
+                                network_xml.bootp(file=pxe_bootp_file,
+                                                  server=pxe_bootp_server)
+                            else:
+                                network_xml.bootp(file=pxe_bootp_file)
         return str(network_xml)
 
     @classmethod