d/t/tgtbasedmpaths: Use stable wwn-* names in autopkgtest

Utkarsh Guptarequested to merge
utkarsh/multipath-tools:stable-wwn into master

These work with or without friendly names, as scsi-${DM_NAME}
is not a stable symlink name. Also, add sleep to allow device creation.

Edited by Utkarsh Gupta

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