Description of problem:
Today, sending discard when removing a disk or a snapshot can be configured on the vdsm configuration file for a host. That means that a host with this property on will send discard calls for each disk/snapshot removal on any block storage domain.
Since the user might want to send discard calls only for some storage domains (those who are built on thin provisioned storage that supports discard), we should change this configuration from host oriented to block storage domain oriented.
Bug tickets must have version flags set prior to targeting them to a release. Please ask maintainer to set the correct version flags and only then set the target milestone.