[POS-14] Implement tryMergeAltChainDo except testMergeAltChain
[POS-14] Implement tryMergeAltChainDo except testMergeAltChain

input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype