Respect snap_name parameter for in-progress backups

[blampe]

Before this change, if any backups were in progress then other snapshot operations driven by the CSI would break.

Concretely, the bug is:

$ curl -H 'Accept: application/json' 'http://piraeus-op-cs.piraeus.svc:3370/v1/remotes/minio/backups?snap_name=INVALID_NAME'
{"linstor":{"pvc-621a06d8-0503-4cf3-84af-d75e1bf40508_back_20220915_234444^snapshot-351f10f6-5b7a-4527-bdd3-0bb7a01bc18a":{"id":"pvc-621a06d8-0503-4cf3-84af-d75e1bf40508_back_20220915_234444^snapshot-351f10f6-5b7a-4527-bdd3-0bb7a01bc18a","start_time":"20220915_234444","start_timestamp":1663285484376,"origin_rsc":"pvc-621a06d8-0503-4cf3-84af-d75e1bf40508","origin_snap":"snapshot-351f10f6-5b7a-4527-bdd3-0bb7a01bc18a","origin_node":"pi4a","vlms":[{"vlm_nr":0,"s3":{"key":"pvc-621a06d8-0503-4cf3-84af-d75e1bf40508_00000_back_20220915_234444^snapshot-351f10f6-5b7a-4527-bdd3-0bb7a01bc18a"}}],"shipping":true,"restorable":false}},"other":{}}

Edit: there also appears to be an issue with getInProgressBackups, because the bug persists even when all backups are successful. I'm not looking into that because the scope of this PR already addresses my immediate problem.

Refs piraeusdatastore/linstor-csi#174