Add an internal field for CloudConfig to make it easier to distinguish.
Instead of creating two CloudConfigs and merging them, just merge the
metadata into the existing CloudConfig.
This attempts to retrieve cloudconfigs from two sources: the meta-data
service, and the user-data service. If only one cloudconfig is found,
that is applied to the system. If both services return a cloudconfig,
the two are merged into a single cloudconfig which is then applied to
the system.
Only a subset of parameters are merged (because the meta-data service
currently only partially populates a cloudconfig). In the event of any
conflicts, parameters in the user-data cloudconfig take precedence over
those in the meta-data cloudconfig.
This uses the new MetadataService implementation to retrieve values for
$private_ipv4 and $public_ipv4 substitutions, instead of using
environment variables.
