Fix incorrect default_groups when parsing projects from XML manifest

Change Details:
* Switch first default group to 'all' instead of 'default'

Change Benefits:
* More consistent with default_groups in the counterpart Save() function
* Fixes bug where command 'repo manifest' added an extra 'default'
  group to every output project element groups attribute. This bug was
  particularly confusing for projects which had 'groups="notdefault"'
  as they were output as 'groups="notdefault,default"' by 'repo manifest'

Change-Id: I5611c027a982d3394899466248b971910bec8c6b
diff --git a/manifest_xml.py b/manifest_xml.py
index f4f6a75..8be83cf 100644
--- a/manifest_xml.py
+++ b/manifest_xml.py
@@ -579,7 +579,7 @@
       groups = node.getAttribute('groups')
     groups = [x for x in re.split('[,\s]+', groups) if x]
 
-    default_groups = ['default', 'name:%s' % name, 'path:%s' % path]
+    default_groups = ['all', 'name:%s' % name, 'path:%s' % path]
     groups.extend(set(default_groups).difference(groups))
 
     if self.IsMirror: