Update Centos7 docker commands
Update Centos7 docker commands

The commands around installing docker on Centos7
in the quickstart guide needed a little tweaking
and a little spell checking.

Change-Id: Ia0367900ab9792a096f753d5fd943ffab0a005a4

coolsvap/kolla,mrangana/kolla,mandre/kolla,GalenMa/kolla,negronjl/kolla,coolsvap/kolla,stackforge/kolla,limamauricio/mykolla,dardelean/kolla-ansible,toby82/kolla,negronjl/kolla,tonyli71/kolla,nihilifer/kolla,stackforge/kolla,rahulunair/kolla,dardelean/kolla-ansible,mandre/kolla,tonyli71/kolla,nihilifer/kolla,openstack/kolla,limamauricio/mykolla,intel-onp/kolla,negronjl/kolla,stackforge/kolla,openstack/kolla,coolsvap/kolla,GalenMa/kolla,rahulunair/kolla,dardelean/kolla-ansible,toby82/kolla,intel-onp/kolla,toby82/kolla,limamauricio/mykolla,mandre/kolla,mrangana/kolla