Quota usage data wrong after instance resized by admin

If the instance of a normal user is resized by admin, the user_id for quota usage will be changed to admin.

Reproduce:
We have two user 'admin' and 'test1' which is a normal user.
1. Create an instance by 'test1', the quota_usage table should be like:
mysql> select * from quota_usages;
+---------------------+---------------------+------------+----+----------------------------------+-----------+--------+----------+---------------+---------+----------------------------------+
| created_at | updated_at | deleted_at | id | project_id | resource | in_use | reserved | until_refresh | deleted | user_id |
+---------------------+---------------------+------------+----+----------------------------------+-----------+--------+----------+---------------+---------+----------------------------------+
| 2014-01-13 08:31:28 | 2014-01-13 08:31:28 | NULL | 7 | 6a47816024ef4860b1a218510a1658a9 | instances | 1 | 0 | NULL | 0 | ea75fd9954244be9b92c2aec99305f63 |
| 2014-01-13 08:31:28 | 2014-01-13 08:31:28 | NULL | 8 | 6a47816024ef4860b1a218510a1658a9 | ram | 512 | 0 | NULL | 0 | ea75fd9954244be9b92c2aec99305f63 |
| 2014-01-13 08:31:28 | 2014-01-13 08:31:28 | NULL | 9 | 6a47816024ef4860b1a218510a1658a9 | cores | 1 | 0 | NULL | 0 | ea75fd9954244be9b92c2aec99305f63 |
+---------------------+---------------------+------------+----+----------------------------------+-----------+--------+----------+---------------+---------+----------------------------------+

2. Resize the instance by admin:
# nova list --all-tenants
+--------------------------------------+------+--------+------------+-------------+-----------------+
| ID | Name | Status | Task State | Power State | Networks |
+--------------------------------------+------+--------+------------+-------------+-----------------+
| a05f62b8-3f14-473c-9d64-b950b4dbfc9e | test | ACTIVE | None | Running | test=10.10.10.2 |
+--------------------------------------+------+--------+------------+-------------+-----------------+

# nova flavor-list
+--------------------------------------+-----------+-----------+------+-----------+------+-------+-------------+-----------+
| ID | Name | Memory_MB | Disk | Ephemeral | Swap | VCPUs | RXTX_Factor | Is_Public |
+--------------------------------------+-----------+-----------+------+-----------+------+-------+-------------+-----------+
| 1 | m1.tiny | 512 | 1 | 0 | | 1 | 1.0 | True |
| 2 | m1.small | 2048 | 20 | 0 | | 1 | 1.0 | True |
| 2ee75e0f-37e1-4561-a5e2-43b8fd677547 | m2.tiny | 512 | 0 | 0 | | 2 | 1.0 | True |
| 3 | m1.medium | 4096 | 40 | 0 | | 2 | 1.0 | True |
| 4 | m1.large | 8192 | 80 | 0 | | 4 | 1.0 | True |
| 5 | m1.xlarge | 16384 | 160 | 0 | | 8 | 1.0 | True |
+--------------------------------------+-----------+-----------+------+-----------+------+-------+-------------+-----------+

# nova resize a05f62b8-3f14-473c-9d64-b950b4dbfc9e 2ee75e0f-37e1-4561-a5e2-43b8fd677547

quota_usage table would create new records with the user_id for the admin.
mysql> select * from quota_usages;
+---------------------+---------------------+------------+----+----------------------------------+-----------+--------+----------+---------------+---------+----------------------------------+
| created_at | updated_at | deleted_at | id | project_id | resource | in_use | reserved | until_refresh | deleted | user_id |
+---------------------+---------------------+------------+----+----------------------------------+-----------+--------+----------+---------------+---------+----------------------------------+
| 2014-01-13 08:31:28 | 2014-01-13 08:31:28 | NULL | 7 | 6a47816024ef4860b1a218510a1658a9 | instances | 1 | 0 | NULL | 0 | ea75fd9954244be9b92c2aec99305f63 |
| 2014-01-13 08:31:28 | 2014-01-13 08:31:28 | NULL | 8 | 6a47816024ef4860b1a218510a1658a9 | ram | 512 | 0 | NULL | 0 | ea75fd9954244be9b92c2aec99305f63 |
| 2014-01-13 08:31:28 | 2014-01-13 08:31:28 | NULL | 9 | 6a47816024ef4860b1a218510a1658a9 | cores | 1 | 0 | NULL | 0 | ea75fd9954244be9b92c2aec99305f63 |
| 2014-01-13 08:39:28 | 2014-01-13 08:39:28 | NULL | 10 | 6a47816024ef4860b1a218510a1658a9 | cores | 0 | 1 | NULL | 0 | ad99c3d4311b4940b083b52fbf73789c |
| 2014-01-13 08:39:28 | 2014-01-13 08:39:28 | NULL | 11 | 6a47816024ef4860b1a218510a1658a9 | instances | 0 | 0 | NULL | 0 | ad99c3d4311b4940b083b52fbf73789c |
| 2014-01-13 08:39:28 | 2014-01-13 08:39:28 | NULL | 12 | 6a47816024ef4860b1a218510a1658a9 | ram | 0 | 0 | NULL | 0 | ad99c3d4311b4940b083b52fbf73789c |
+---------------------+---------------------+------------+----+----------------------------------+-----------+--------+----------+---------------+---------+----------------------------------+