Fix premature exit in storage_rebalance.rb

Fix premature exit in storage_rebalance.rb

With each project we migrate, we shrink the set we're selecting from (as we're selecting by repository_storage) while advancing the pagination index forward at a constance pace. At some point we're going request a page that's outside the shrunk set, getting empty list in response. Here we do a start-over from page 1 whenever we think we reached the end of the set, and only exiting when we get two empty responses in a row.