mute useless console output, when run ./stack.sh
mute useless console output, when run ./stack.sh

Run ./stack.sh will dump ~400 lines of information, because of
tar xvfz pip-*.tar.gz, and python setup.py install.

We'd better mute stdout for the two steps, to make console cleaner

Change-Id: Icf87947e020acb48d8cbe4cdcc1641f060e50f6d

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