The configuration server listens on a Unix socket for connections from
the node daemon.  The node daemon sends the instance parameters to the
configuration server so they can be served through the metadata daemon
web server to the instances which have the communication mechanism
enabled.

The configuration server reads the instance parameters and, currently,
it extracts the instance's name and the instance's IP address on the
instance communication NIC.  The instance's name is used for logging
and the IP address is used to index the instance parameters, given
that instances do not authenticate with the metadata daemon, and the
only thing we know about them is their IP address.

The configuration server also extracts the OS parameters, including
public, private and secret, and creates an object containing those
parameters and their visibility.

The configuration is kept internally in an 'MVar' which will be shared
with the metadata daemon web server.

Signed-off-by: Jose A. Lopes <jabolopes@google.com>
Reviewed-by: Hrvoje Ribicic <riba@google.com>