Fix type is overwritten when UPDATE cell without type specified

If you not specified the 'cell-type' in UPDATE request,
  the value will be overwritten by the default value, 'child'.
That's not correct, you need to reserve the existing cell-type.

The issue is also involved in the new V3-api.

Fixes bug: 1224461

Change-Id: I5c5043b9e5e0c33995422094284c3f19aac78593
Merge "Fix type is overwritten when UPDATE cell without type specified"