Use $((EXPRESSION)) instead of $[EXPRESSION]
Use $((EXPRESSION)) instead of $[EXPRESSION]

$((EXPRESSION)) is POSIX-conform and should be preferred.

Change-Id: Ibd0524194aeda40961e202b6761dbaed2ea27dfa

NaohiroTamura/diskimage-builder,eantyshev/diskimage-builder,zioproto/diskimage-builder,takahashinobuyuki/diskimage-builder,switch-ch/diskimage-builder,rdo-management/diskimage-builder,varunarya10/diskimage-builder,takahashinobuyuki/diskimage-builder,zioproto/diskimage-builder,CSC-IT-Center-for-Science/diskimage-builder,eantyshev/diskimage-builder,varunarya10/diskimage-builder,openstack/diskimage-builder,CSC-IT-Center-for-Science/diskimage-builder,JioCloud/diskimage-builder,switch-ch/diskimage-builder,NaohiroTamura/diskimage-builder,JioCloud/diskimage-builder,openstack/diskimage-builder,rdo-management/diskimage-builder