virtconv: Don't create default pool when in dry mode

We will still need to create pools to probe source storage if doing
--print-xml.

virtconv/formats.py

@@ -270,7 +270,7 @@ class VirtConverter(object):
             disk_format = None
 
         if destdir is None:
-            destdir = StoragePool.get_default_path(self.conn)
+            destdir = StoragePool.get_default_path(self.conn, build=not dry)
 
         guest = self.get_guest()
         for disk in guest.get_devices("disk"):

virtinst/storage.py

@@ -213,7 +213,7 @@ class StoragePool(_StorageObject):
 
 
     @staticmethod
-    def get_default_path(conn):
+    def get_default_path(conn, build=True):
         """
         Return the default storage path. If there's a 'default' pool,
         report that. If there's no default pool, return the path we would
@@ -230,7 +230,9 @@ class StoragePool(_StorageObject):
         except:
             pass
 
-        return StoragePool.build_default_pool(conn).target_path
+        if build:
+            return StoragePool.build_default_pool(conn).target_path
+        return _get_default_pool_path(conn)
 
 
     @staticmethod