In some deployement environments, nova compute processes took a bit
longer to register on all hosts, and vm/server is instantiated almost
immediately before the process is registered on remaining hosts.
This PS enhances the cell-setup-init script to enable option to
extend the wait before performing discover hosts.
Change-Id: Ie9867e64c554d4f39fdc7432823a1869f0b4a520
6b785b16dc