refactor test script
refactor test script

- fix status code (script exited with success even with failing tests)
- clean up and explain things

pash7ka/zeppelin-solidity,OpenZeppelin/openzeppelin-contracts,OpenZeppelin/zep-solidity,OpenZeppelin/openzeppelin-contracts,pash7ka/zeppelin-solidity,OpenZeppelin/zep-solidity,OpenZeppelin/openzeppelin-contracts,dmx374/zeppelin-solidity,dmx374/zeppelin-solidity,OpenZeppelin/zeppelin-solidity,OpenZeppelin/zeppelin-solidity