MT#8287 only create aliases if available on subscriber creation

some input validation, fixes issues on subadmin subscriber creation

(cherry picked from commit c15acb942384c7a1847a225346a0bc6a54e9d8fa)
MT#8287 fix subscriber termination by subadmin

(cherry picked from commit ef713a8f843cd8b54b2f40b9f4ecd87a78b1674b)