Merge branch 'stable-2.1' into devel-2.1

* stable-2.1:
  TLReplaceDisks: Delay iallocator when evacuating node
  Implement debug level across OS-related RPC calls
  Second try to fix LUVerifyCluster
  LUVerifyCluster: Fix bug with offline nodes
  utils: Fix retry delay calculator
  Bump RPC protocol version to 30

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>