An ACL granted testuser tried to download an object from the `AUTH_ABC/driveeval-artifacts-stage-project-johndoe-ai` but it failed while SLO middleware retrieving segment from segment container since the segment container has not ACL permission granted to the `testuser`.
* The response code 500 confuses users.
* Shouldn't SLO middleware ignore the ACL while retrieving SLO segment?
```
Nov 25 16:46:37 ss0158 proxy-server: 10.150.134.72 10.150.134.72 25/Nov/2019/16/46/37 GET /v1/AUTH_ABC/driveeval-artifacts-stage-project-johndoe-ai/test/4e424bc2-7474-5cb9-9ca2-615cf71a87e6/root/6e207b06-1f4f-5fab-a207-f472aae1c307/roadrunner/roadcast_20191120_192905.log HTTP/1.0 206 - Go-http-client/1.1 nvetl%2Cs3 - 784 - txf9d2c07da9674687bcca4-005ddc056d - 0.0139 S3 - 1574700397.279757023 1574700397.293642998 0
Nov 25 16:46:37 ss0158 proxy-server: - - 25/Nov/2019/16/46/37 GET /v1/AUTH_ABC/driveeval-artifacts-stage-project-johndoe-ai%252Bsegments/test/4e424bc2-7474-5cb9-9ca2-615cf71a87e6/root/6e207b06-1f4f-5fab-a207-f472aae1c307/roadrunner/roadcast_20191120_192905.log/YjA4NTI5OTUtY2JlMS00ZmYyLWE2YTctNzBiNzA5N2FlNzAw/1%3Fmultipart-manifest%3Dget HTTP/1.0 499 - Go-http-client/1.1%20%20SLO%20MultipartGET nvetl%2Cs3 - 73 - txf9d2c07da9674687bcca4-005ddc056d - 0.0045 SLO - 1574700397.296395063 1574700397.300894022 0
Nov 25 16:46:37 ss0158 proxy-server: While processing manifest /v1/AUTH_ABC/driveeval-artifacts-stage-project-johndoe-ai/test/4e424bc2-7474-5cb9-9ca2-615cf71a87e6/root/6e207b06-1f4f-5fab-a207-f472aae1c307/roadrunner/roadcast_20191120_192905.log, got 403 while retrieving /v1/AUTH_ABC/driveeval-artifacts-stage-project-johndoe-ai%2Bsegments/test/4e424bc2-7474-5cb9-9ca2-615cf71a87e6/root/6e207b06-1f4f-5fab-a207-f472aae1c307/roadrunner/roadcast_20191120_192905.log/YjA4NTI5OTUtY2JlMS00ZmYyLWE2YTctNzBiNzA5N2FlNzAw/1 (txn: txf9d2c07da9674687bcca4-005ddc056d)
Nov 25 16:46:37 ss0158 proxy-server: InternalError: 500 Internal Server Error (unexpected status code 409):
Traceback (most recent call last):
File "/opt/ss/lib/python2.7/site-packages/swift/common/middleware/s3api/s3api.py", line 244, in __call__
resp = self.handle_request(req)
File "/opt/ss/lib/python2.7/site-packages/swift/common/middleware/s3api/s3api.py", line 280, in handle_request
res = handler(req)
File "/opt/ss/lib/python2.7/site-packages/swift/common/middleware/s3api/controllers/obj.py", line 112, in GET
return self.GETorHEAD(req)
File "/opt/ss/lib/python2.7/site-packages/swift/common/middleware/s3api/controllers/obj.py", line 81, in GETorHEAD
resp = req.get_response(self.app)
File "/opt/ss/lib/python2.7/site-packages/swift/common/middleware/s3api/s3request.py", line 1394, in get_response
headers, body, query)
File "/opt/ss/lib/python2.7/site-packages/swift/common/middleware/s3api/s3request.py", line 1378, in _get_response
raise InternalError('unexpected status code %d' % status)
InternalError: InternalError: 500 Internal Server Error (unexpected status code 409) (txn: txf9d2c07da9674687bcca4-005ddc056d)
Nov 25 16:46:37 ss0158 proxy-server: 10.150.134.72 10.150.134.72 25/Nov/2019/16/46/37 GET /driveeval-artifacts-stage-project-johndoe-ai/test/4e424bc2-7474-5cb9-9ca2-615cf71a87e6/root/6e207b06-1f4f-5fab-a207-f472aae1c307/roadrunner/roadcast_20191120_192905.log HTTP/1.0 500 - Go-http-client/1.1 - - 182 - txf9d2c07da9674687bcca4-005ddc056d - 0.0297 - - 1574700397.274795055 1574700397.304544926 -A
```
