[swift] left slo file segment after delete manifest

[Bulat Gaifullin]

On swift are enabled erasure codes (10х4, 10 chunks are spread across 4 servers)

Steps to reproduce:
1. create slo file with one segment
2. append 1 addition segment to slo file (now file has 2 segments)
3. copy file (curl -i https://192.168.10.11/v1/AUTH_4a97d73cc4c249d7ae03f9b74dff3384/fast/test_file.txt?multipart-manifest=get COPY -H "Destination: fast/test_file.txt.bak" -H "X-Auth-Token: gAAAAABcjih69pbr..."
4. delete origin file (only manifest) curl -i https://192.168.10.11/v1/AUTH_4a97d73cc4c249d7ae03f9b74dff3384/fast/test_file.txt DELETE -H "X-Auth-Token: gAAAAABcjih69pbr..."
5. delete copy of file (with segments) curl -i https://192.168.10.11/v1/AUTH_4a97d73cc4c249d7ae03f9b74dff3384/fast/test_file.txt.bak?multipart-manifest=delete DELETE -H "X-Auth-Token: gAAAAABcjih69pbr..."

*Expected*:

manifest and all segments are removed

*Actual*:
RESP BODY: Number Deleted: 2
Number Not Found: 0
Response Body:
Response Status: 400 Bad Request
Errors:
/fast_segments/test_file.txt/slo/1552820364.21/64000000/00000001, 409 Conflict

and segment /fast_segments/test_file.txt/slo/1552820364.21/64000000/00000001 does not deleted