cross chain test assertions

[coderfi]

• use testify/assert
• add various assertions to trust_node_test.go
• return statements in DoLoop (for testing validation)
• add truffle console notes in README.md
• fix keystore relative path
• update build-docker.sh to echo the image name at the end, overridable version
• add helper targets to Makefile
• TestRopstenNativeETH() - test fails, needs keys updates, performs additional validation
• TestRopstenERC20Token() - test fails, needs dev updates
• TestWithdrawal() - test succeeds, performs additional validation