Remove usage of $[ for arithmetic
Remove usage of $[ for arithmetic

$[ is deprecated for the more familiar $((

Required when bash8 starts testing from tox and [1] goes in

[1] https://review.openstack.org/#/c/117430/

Change-Id: I8ba180be036836f37ebdbb6da36ff0be486c043e

sc68cal/devstack,richliu/devstack,openstack-dev/devstack,LoHChina/devstack,parul24/devstack,mmasaki/devstack,LoHChina/devstack,nuxeh/devstack,kplus/devstack-moonshot,richliu/devstack,wenhuizhang/devstack,dirkmueller/devstack,bq-xiao/devstack,eshnil2000/devstack,bigswitch/devstack,avvocatodemarchis/devstack,sc68cal/devstack,BSJAIN92/OpenStack,thomasem/devstack,NaokiMiyata/devstack,promptworks/devstack,bswartz/devstack,pczerkas/devstack,pacinete/devstack,vishnugonela/devstack,bswartz/devstack,bq-xiao/devstack,vsham20/devstack,andrewrothstein/devstack,pczerkas/devstack,bigswitch/devstack,BSJAIN92/OpenStack,rushiagr/devstack,vishnugonela/devstack,prithivm/branch01,flavio-fernandes/devstack,varunarya10/devstack,mc2014/devstack,Mahito/devstack,herrsechs/devstack,neerja28/Devstack_GlusterFS,ozamiatin/devstack,NaokiMiyata/devstack,ozamiatin/devstack,upadhyay-prashant/devstack,eharney/devstack,bljgaurav/openstack-test,pombredanne/devstack,virtualopensystems/devstack,atulpatil301/devstack,herrsechs/devstack,pombredanne/devstack,samgoon/devstack,j4/devstack,neerja28/Devstack_GlusterFS,avvocatodemarchis/devstack,dtroyer/devstack,nawawi/openstack,affo/devstack,HPCHub/devstack,group-policy/devstack,TwinkleChawla/devstack,eharney/devstack,mc2014/devstack,olivierlemasle/devstack,thomasem/devstack,group-policy/devstack,olivierlemasle/devstack,wenhuizhang/devstack,promptworks/devstack,TwinkleChawla/devstack,atulpatil301/devstack,pacinete/devstack,Mahito/devstack,noironetworks/devstack,prithivm/branch01,tianweizhang/devstack,liuquansheng47/devstack,bljgaurav/openstack-test,affo/devstack,dtroyer/devstack,costingalan/devstack,andrewrothstein/devstack,vsham20/devstack,noironetworks/devstack,mmasaki/devstack,CloudServer/devstack,j4/devstack,flavio-fernandes/devstack,dirkmueller/devstack,sequenceiq/devstack,samgoon/devstack,tianweizhang/devstack,nawawi/openstack,HPCHub/devstack,rushiagr/devstack,mssumanth/devstack,varunarya10/devstack,parul24/devstack,mssumanth/devstack,CloudServer/devstack,upadhyay-prashant/devstack,openstack-dev/devstack,nuxeh/devstack,liuquansheng47/devstack,kplus/devstack-moonshot,sequenceiq/devstack,costingalan/devstack