Change resource generation type

Use eval_generate to generate swift rings.
This will ensure that Ring_devices resource
is completed only when all the Ring_*_devices
is finished, thus ensuring that rebalance begins
only after all the devices were created.

Also pin services start to rebalance end.

Change-Id: If8c64a565ebb86f545add145934d566d666ef073
Closes-bug: #1305826