Update qemu package name for Ubuntu aarch64
Update qemu package name for Ubuntu aarch64

The qemu-system package, and not qemu-kvm, should be installed on either
trusty- or utopic-based ARMv8 (aarch64) Ubuntu releases. Additionally,
libguestfs is not available so that is not installed.

No changes are required for vivid.

Change-Id: Id9dc1fc465bd7acab17c991c292fb531016758ad
Signed-off-by: Andrew McDermott <c25a3c73764b1b7ccb7bc02426e7ac8af5e6f88d@linaro.org>

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