Add CentOS-7 image name for AWS.
Add CentOS-7 image name for AWS.

hackday-profilers/flocker,w4ngyi/flocker,jml/flocker,moypray/flocker,AndyHuu/flocker,mbrukman/flocker,lukemarsden/flocker,wallnerryan/flocker-profiles,adamtheturtle/flocker,moypray/flocker,runcom/flocker,w4ngyi/flocker,adamtheturtle/flocker,agonzalezro/flocker,Azulinho/flocker,adamtheturtle/flocker,Azulinho/flocker,1d4Nf6/flocker,lukemarsden/flocker,wallnerryan/flocker-profiles,wallnerryan/flocker-profiles,agonzalezro/flocker,achanda/flocker,mbrukman/flocker,w4ngyi/flocker,Azulinho/flocker,1d4Nf6/flocker,achanda/flocker,moypray/flocker,jml/flocker,AndyHuu/flocker,lukemarsden/flocker,achanda/flocker,runcom/flocker,runcom/flocker,hackday-profilers/flocker,agonzalezro/flocker,AndyHuu/flocker,LaynePeng/flocker,1d4Nf6/flocker,jml/flocker,hackday-profilers/flocker,mbrukman/flocker,LaynePeng/flocker,LaynePeng/flocker