Description of problem:
master domain fail to regress to regular domain after storage pool destroyed

Version-Release number of selected component (if applicable):
vdsm-4.9.4-0.18

How reproducible:
often

Steps to Reproduce:
(1)create storage domain sd1
(2)create storage pool with md sd1
(3)destroy storage pool
(4)get sd1 info
  
Actual results:
storage domain's role is still master and it's pool is not cleared

Expected results:
storage domain's role regress to regular and it's pool should be cleared

Additional info:
 { "resource": "storagedomain",
   "id": "ae4d6a96-d3da-419c-8905-b5eec55c4500",
"href": "/vdsm-api/storagedomains/ae4d6a96-d3da-419c-8905-b5eec55c4500",
"name": "Test Domain",
"type": "LOCALFS",
"class": "Data",
"role": "Master",----------------------------------->wrong
"remotePath": "/storagedomain7",
"version": "0",
"master_ver": "1",
"lver": "0",
"spm_id": "1",
"storagepool": { "id": "1ef32ac7-1e12-4823-8e8c-8c887333fe50", "href": "/vdsm-api/storagepools/1ef32ac7-1e12-4823-8e8c-8c887333fe50" },------------------------------->wrong
"actions": {}

}