To maintain the behavior of the coreos-setup-environment that has
started to move into cloudinit we need to write out /etc/environment
with the public and private addresses, if known. The file is updated so
that other contents are not replaced. This behavior is disabled entirely
if /etc/environment was written by a write_files entry.
This uses the new MetadataService implementation to retrieve values for
$private_ipv4 and $public_ipv4 substitutions, instead of using
environment variables.
Move the old metadata-service datasource to url datasource. This new datasource
checks for the existance of meta-data.json and if it doesn't exist, walks the
meta-data directory to build a metadata blob.
This change creates a few simple interfaces for coreos-specific
configuration options and moves things to them wherever possible; so if
an option needs to write a file, or create a unit, it is acted on
exactly the same way as every other file/unit that needs to be written
during the cloud configuration process.
