update gtest-parallel-bitcoin with upstream features & fixes
update gtest-parallel-bitcoin with upstream features & fixes

- timeout option (`--timeout secs`)
- JSON file output option (`--dump_json_test_results=FILE`)

The above have been tested lightly and I didn't find any interaction problems.
The output of the script is improved too.

Two options relating to some multi-machine sharding have been added.
It doesn't appear to call out to machines though, so I assume it is a feature used by Google's own test environment. I have not tested it myself, but didn't see a reason to remove it either, in case it's useful to somebody.

Bitcoin-com/BUcash,Justaphf/BitcoinUnlimited,BTCfork/hardfork_prototype_1_mvf-bu,BitcoinUnlimited/BitcoinUnlimited,Bitcoin-com/BUcash,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,BitcoinUnlimited/BitcoinUnlimited,BTCfork/hardfork_prototype_1_mvf-bu,Bitcoin-com/BUcash,BTCfork/hardfork_prototype_1_mvf-bu,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,Bitcoin-com/BUcash,Justaphf/BitcoinUnlimited,Justaphf/BitcoinUnlimited,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,BTCfork/hardfork_prototype_1_mvf-bu,BitcoinUnlimited/BitcoinUnlimited,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,Bitcoin-com/BUcash,BTCfork/hardfork_prototype_1_mvf-bu,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,BTCfork/hardfork_prototype_1_mvf-bu,Bitcoin-com/BUcash,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu,Justaphf/BitcoinUnlimited,ftrader-bitcoinunlimited/hardfork_prototype_1_mvf-bu