Complete tests and doc to release go package vendoring

[jt-nti]

Follow on from PR #86

Tests in test/go-chaincode/vendor-dependencies.bats should confirm the expected behaviour for possible .govendor_packages files (is this a standard Go file or something specific to starter kit?), e.g. no file, empty file, entries with leading/trailing/no whitespace, etc.

Also needs some sort of documentation in https://github.com/IBM-Blockchain-Starter-Kit/IBM-Blockchain-Starter-Kit.github.io

Should there be a placeholder file with suitable comment in the bootstrap project as well?