Implement automatic discovery and bootstrap for cf-agent.

cf-agent discovers policy servers using Avahi implementation of Zeroconf protocol
at runtime using dlopen.

If a single hub is discovered cf-agent will automaticaly bootstrap to it.

If there's more than one hub discovered cf-agent will print a message listing
available hub and ask user to manualy bootstrap to a proper IP address using
--bootstrap --policy-server <right IP address> command line option.

To use automatic bootstrap --bootstrap/-B command line option is required without
specifying the IP address.
Implement generation of Avahi configuration file.

Add new command line option to cf-serverd -A. cf-serverd executed
with this option will generate Avahi configuration file in
/etc/avahi/services and restart avahi-daemon to make policy server
discoverable over the network.
Code cleanup for automatic bootstrap
Register atexit function to close loaded library.