Integration tests (#805)

* Started substrate tests

* Sync test

* Test updates

* Improved tests

* Use on-chain block delay

* Parallel test execution

* Otimized tests

* Logging

* Fixed racing test

* Fixed compilation

* Fixed timestamp test

* Removed rlp dependency

* Minor fixes

* Fixed tests

* Removed best_block_id and resolved fdlimit issue

* Whitespace

* Use keyring

* Style

* Added API execution setting

* Removed stale import