remove spaces after open parens
check the return value of `fwrite`
Merge pull request #2460 from cremno/mrb_dump_irep_binary-report-fwrite-failure

check the return value of `fwrite`
Run mrbgem and core tests on minimum dependencies.
Solves #2355.

In test drivers:
* Uses `mrb_t_pass_result` to check and pass test result to main `mrb_state`.
* Adds `mrb_init_test_driver` to init test `mrb_state`.