xmlbuilder: Make embedded device XML print correctly

If you call get_xml() on a device that's part of a Guest class,
the last element has correct indent but not the first element.

Steal the indent from the last element and prepend it to the returned
XML

Signed-off-by: Cole Robinson <crobinso@redhat.com>

tests/data/cli/compare/virt-xml-update-nodefine-succeed.xml

@@ -11,7 +11,7 @@
    </devices>
  </domain>
 
-<interface type="user">
+    <interface type="user">
       <mac address="00:11:22:33:44:55"/>
       <model type="e1000"/>
     </interface>

tests/data/cli/compare/virt-xml-update-succeed.xml

@@ -11,7 +11,7 @@
    </devices>
  </domain>
 
-<interface type="user">
+    <interface type="user">
       <mac address="00:11:22:33:44:55"/>
       <model type="e1000"/>
     </interface>

tests/test_xmlparse.py

@@ -1030,11 +1030,11 @@ def testXMLBuilderCoverage():
     xml = conn.lookupByName("test-for-virtxml").XMLDesc(0)
     guest = virtinst.Guest(conn, parsexml=xml)
 
-    assert guest.features.get_xml().startswith("<features")
-    assert guest.clock.get_xml().startswith("<clock")
+    assert guest.features.get_xml().startswith("  <features")
+    assert guest.clock.get_xml().startswith("  <clock")
     assert guest.seclabels[0].get_xml().startswith("<seclabel")
-    assert guest.cpu.get_xml().startswith("<cpu")
-    assert guest.os.get_xml().startswith("<os")
+    assert guest.cpu.get_xml().startswith("  <cpu")
+    assert guest.os.get_xml().startswith("  <os")
     assert guest.cpu.get_xml_id() == "./cpu"
     assert guest.cpu.get_xml_idx() == 0
     assert guest.get_xml_id() == "."

virtinst/xmlbuilder.py

@@ -586,7 +586,14 @@ class XMLBuilder(object):
         self._add_parse_bits(xmlapi)
         ret = xmlapi.get_xml(self._xmlstate.make_abs_xpath("."))
 
-        if ret and not ret.endswith("\n"):
+        if not ret:
+            return ret
+
+        lastline = ret.rstrip().splitlines()[-1]
+        if not ret.startswith(" ") and lastline.startswith(" "):
+            ret = lastline.split("<")[0] + ret
+
+        if not ret.endswith("\n"):
             ret += "\n"
         return ret