References: bsc#1091113
In Tumbleweed the .treeinfo file has no version as it is mostly meaningless.

Index: virt-manager-1.5.0/virtinst/urlfetcher.py
===================================================================
--- virt-manager-1.5.0.orig/virtinst/urlfetcher.py
+++ virt-manager-1.5.0/virtinst/urlfetcher.py
@@ -1136,7 +1136,10 @@ class SuseDistro(Distro):
                    "Open Enterprise" in family and 'oes' in self.urldistro:
                     ret = True
             if ret:
-                version = self.treeinfo.get("general", "version")
+                if 'Tumbleweed' not in family:
+                    version = self.treeinfo.get("general", "version")
+                else:
+                    version = "tmblweed"
                 distro_version = ['VERSION', version]
                 self.version_from_content = distro_version
                 self._variantFromVersion()