Incorrect exception raised during create image , when invalid Image Metadata is passed

Our tempest test that validates a return error code when an invalid key-value pair for metadata is passed during Create Image fails for the following scenarios.

1. Blank key-value metadata

Steps to reproduce:
1. Create a server
2. Create an image of the above server and pass invalid metadata key value pair, for ex:
meta = {'': ''}

Expected Return Code: 400 BadRequest
Actual Return Code: 404 Not Found

Besides, in this case the snapshot image is created but the operation stays in Queued state.

2. Metadata that exceeds length limit

Steps to reproduce:
1. Create a server
2. Create an image of the above server and pass invalid metadata key value pair, for ex:
meta = {'a' * 260: 'b' * 260}

Expected Return Code: 413 OverLimit
Actual Return Code: 404 Not Found

Return an error when creating image with invalid metadata ... FAIL
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FAIL: Return an error when creating image with invalid metadata
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Traceback (most recent call last):
  File "/opt/stack/tempest/tests/test_images.py", line 276, in test_create_image_specify_invalid_metadata
    self.fail("Should raise 400 Bad Request if meta data is invalid")
AssertionError: Should raise 400 Bad Request if meta data is invalid
-------------------- >> begin captured logging << --------------------
tempest.config: INFO: Using tempest config file /opt/stack/tempest/etc/tempest.conf
tempest.common.rest_client: ERROR: Request URL: http://10.2.3.164:8774/v2/e5eb2e14ed8a409d9b36db3fddb5a757/images/9ea13f87-88ff-420c-8822-4d7ee7352d51
tempest.common.rest_client: ERROR: Request Body: None
tempest.common.rest_client: ERROR: Response Headers: {'date': 'Mon, 28 May 2012 07:21:44 GMT', 'status': '404', 'content-length': '62', 'content-type': 'application/json; charset=UTF-8', 'x-compute-request-id': 'req-921eda64-cfe2-43ff-a892-8fac1e9f9d67'}
tempest.common.rest_client: ERROR: Response Body: {"itemNotFound": {"message": "Image not found.", "code": 404}}
--------------------- >> end captured logging << ---------------------

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Return an error when creating image with meta data over 256 chars ... FAIL

======================================================================
FAIL: Return an error when creating image with meta data over 256 chars
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/opt/stack/tempest/tests/test_images.py", line 293, in test_create_image_specify_metadata_over_limits
    self.fail("Should raise 413 Over Limit if meta data was too long")
AssertionError: Should raise 413 Over Limit if meta data was too long
-------------------- >> begin captured logging << --------------------
tempest.config: INFO: Using tempest config file /opt/stack/tempest/etc/tempest.conf
tempest.common.rest_client: ERROR: Request URL: http://10.2.3.164:8774/v2/e5eb2e14ed8a409d9b36db3fddb5a757/images/9ea13f87-88ff-420c-8822-4d7ee7352d51
tempest.common.rest_client: ERROR: Request Body: None
tempest.common.rest_client: ERROR: Response Headers: {'date': 'Mon, 28 May 2012 13:11:13 GMT', 'status': '404', 'content-length': '62', 'content-type': 'application/json; charset=UTF-8', 'x-compute-request-id': 'req-4d383155-65f3-4eb3-8196-4adb91674853'}
tempest.common.rest_client: ERROR: Response Body: {"itemNotFound": {"message": "Image not found.", "code": 404}}
--------------------- >> end captured logging << ---------------------

----------------------------------------------------------------------

Ran 2 test in 51.507s

FAILED (failures=2)