Merge pull request #193 from benjic/cloudconfig_variables

docs(quick-start): Clarified use of fields in cloud config
feat(datasource): PoC implementation for the CloudSigma server context
feat(*): Add the server context datasource in the main flags
refactor: Add ExtractIPs method to the Datasource interface
test: Add tests and simplify the userdata crunching
refactor: Fetch byte arrays from the serial console

That allows me use native IP guessing
refactor: Put cepgo in the source tree
refactor: Remove leftover ExtractIPs method in remoteFile
refactor: Rename the server context flag to cloudsigma-metadata
refactor: Add goserial in third party modules