script: refactor avoiding duplicating logic in boostrap local chain

[huyngopt1994]

INFO [12-25|17:11:00.048] Commit new mining work                   number=11 sealhash=921cc9..8bde0b uncles=0 txs=0 gas=0 fees=0 elapsed=2.828ms
INFO [12-25|17:11:00.048] Sealing block with                       number=11 delay=4.951728s headerDifficulty=3 val=0x1Feac05E5aE02CB3F7A25E010F70fec4aC6e2272 txs=0
INFO [12-25|17:11:00.103] New local node record                    seq=1,735,121,428,494 id=b152b046f7dbc277 ip=127.0.0.1 udp=30305 tcp=30305
INFO [12-25|17:11:03.017] SubmitBlockReward
INFO [12-25|17:11:03.033] Imported new chain segment               blocks=1 txs=0 mgas=0.000 elapsed=16.519ms    mgasps=0.000 number=11 hash=fe8a48..04fdbb dirty=0.00B
INFO [12-25|17:11:03.034] SubmitBlockReward
INFO [12-25|17:11:03.034] Commit new mining work                   number=12 sealhash=f6dede..b384bd uncles=0 txs=0 gas=0 fees=0 elapsed="170.5µs"
INFO [12-25|17:11:03.034] Sealing block with                       number=12 delay=2.965516s headerDifficulty=7 val=0x1Feac05E5aE02CB3F7A25E010F70fec4aC6e2272 txs=0
INFO [12-25|17:11:06.011] Successfully sealed new block            number=12 sealhash=f6dede..b384bd hash=5b0f2e..07e5e1 elapsed=2.977s      txs=0
INFO [12-25|17:11:06.012] 😱 block lost                             number=5  hash=38815e..5ef0fe
INFO [12-25|17:11:06.012] 🔨 mined potential block                  number=12 hash=5b0f2e..07e5e1
INFO [12-25|17:11:06.012] Slash
INFO [12-25|17:11:06.012] SubmitBlockReward
INFO [12-25|17:11:06.013] Commit new mining work                   number=13 sealhash=f90dbb..42ad4d uncles=0 txs=0 gas=0 fees=0 elapsed=1.962ms
WARN [12-25|17:11:06.014] Block sealing failed                     err="signed recently, must wait for others" height=13

Make script more dynamically and avoiding duplicating.