Resolved the deployer cann't connect to agent error

When do deploy micro bosh, there is a deadlock between agent running in
stemcell vm and deployer.

So, I adjusted the sequence of the deployer process in order that
deployer could create & attach volume to stemcell vm first and then
waiting for agent done.

Also we can change the process in agent, but because of agent is
builded in stemcell image, I think it's not a graceful way considering
compatibility

issue detailis are in https://github.com/cloudfoundry/bosh/issues/159