cli: Add --serial target.model.name=

This maps to XML like:

  <serial>
    <target>
      <model name='X'/>
    </target>
  </serial>

tests/cli-test-xml/compare/virt-install-many-devices.xml

@@ -266,6 +266,9 @@
       <source mode="bind" host="127.0.0.1" service="2222"/>
       <protocol type="telnet"/>
       <log file="/tmp/foo.log" append="on"/>
+      <target>
+        <model name="pci-serial"/>
+      </target>
     </serial>
     <serial type="nmdm">
       <source master="/dev/foo1" slave="/dev/foo2"/>

tests/clitest.py

@@ -533,7 +533,7 @@ c.add_compare("""
 --input type=keyboard,bus=usb
 --input tablet
 
---serial tcp,host=:2222,mode=bind,protocol=telnet,log_file=/tmp/foo.log,log_append=yes
+--serial tcp,host=:2222,mode=bind,protocol=telnet,log_file=/tmp/foo.log,log_append=yes,,target.model.name=pci-serial
 --serial nmdm,source.master=/dev/foo1,source.slave=/dev/foo2
 --parallel udp,host=0.0.0.0:1234,bind_host=127.0.0.1:1234
 --parallel unix,path=/tmp/foo-socket,source.seclabel0.model=none,source.seclabel1.model=dac,source.seclabel1.relabel=yes,source.seclabel1.label=foobar,source.seclabel.relabel=no

virtinst/cli.py

@@ -3439,6 +3439,7 @@ class _ParserChar(VirtCLIParser):
         cls.add_arg("target.type", "target_type")
         cls.add_arg("target.name", "target_name")
         cls.add_arg("target.port", "target_port")
+        cls.add_arg("target.model.name", "target_model_name")
 
 
 class ParserSerial(_ParserChar):

virtinst/devices/char.py

@@ -161,6 +161,7 @@ class _DeviceChar(Device):
     target_type = XMLProperty("./target/@type")
     target_name = XMLProperty("./target/@name")
     target_state = XMLProperty("./target/@state")
+    target_model_name = XMLProperty("./target/model/@name")
 
 
     ##################