This brings in a few major fixes:

• allocator: Avoid assigning duplicate IPs during initialization (allocator: Avoid assigning duplicate IPs during initialization swarmkit#2237)
• orchestrator: Check that service's SpecVersion exists before dereferencing (orchestrator: Check that service's SpecVersion exists before dereferencing swarmkit#2233)
• Avoid nil Allocator in controlapi (Avoid nil Allocator in controlapi swarmkit#2240)
• [ca] When rotating the root CA, ignore the node membership ([ca] When rotating the root CA, ignore the node membership swarmkit#2218)