Tools metadata in simplestreams format can be parsed and validated. A new environs/tools package is created, and the existing environs/tools.go is moved there, and the new simplestreams support added also. The agent/tools package is disambiguated as agenttools where there were clashes.
The metadata plugin is extended to support validating tools metadata in the same way as image metadata. The next branches will support using the tools metadata when finding tools to bootstrap with.