Refactor _wait_for_volume_state_change.
Refactor _wait_for_volume_state_change.

agonzalezro/flocker,AndyHuu/flocker,mbrukman/flocker,hackday-profilers/flocker,AndyHuu/flocker,agonzalezro/flocker,w4ngyi/flocker,AndyHuu/flocker,w4ngyi/flocker,agonzalezro/flocker,hackday-profilers/flocker,mbrukman/flocker,mbrukman/flocker,hackday-profilers/flocker,w4ngyi/flocker,wallnerryan/flocker-profiles,wallnerryan/flocker-profiles,wallnerryan/flocker-profiles