Revert "Read current vbucket map."

This reverts commit ea6fe2ea5a3dd19b9a9ffa51a9833ad4959eb522.
Correctly check feasibility of chains with num_replicas=1.
Merge commit '541744bb815a7d5d6b1b8124dd2604f3b3c9cdbb'

* commit '541744bb815a7d5d6b1b8124dd2604f3b3c9cdbb':
  Revert "Read current vbucket map."
Merge branch 'for-3.0'

* for-3.0:
  Correctly check feasibility of chains with num_replicas=1.