test: use pgrep for better compatibility
test: use pgrep for better compatibility

pidof is not available on BSD system, while pgrep is present on BSD, Linux and macOS


Former-commit-id: 2e89feec9257e5a340c6430e598f60e8ae073086
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin