5.0.2 ship: sending the start block from chain_state_history blocks everything else

[cc32d9]

I tried initializing Chronicle in Europe from a ship server in the US. The initial state block in EOS is about 5GB, so it takes a while to transfer across the Atlantic.

While sending the initial block, nodeos stopped all other activities: responding on API and processing new blocks via p2p. The CPU and storage weren't busy much because of the geographical distance.