Fix volume_id's type.
Fix volume_id's type.

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