libvirt: support for a separate deployment network interface

Setting 'deploy_if=eth1' will attempt to autodiscover the IP address
of the given NIC and use it as the deployment 'host' address.
vc: fix "vc checkpoint" to work with large number of changes

Failed earlier with "OSError: [Errno 7] Argument list too long"
if the number of deleted items was too big.
tool: suppress argh warnings about installing 'argcomplete'
make: fix "make deb" to work on debian wheezy
core: remove an extra stat() from iter_configs()
misc: whitespace fixes
tool: faster "poni list" by skipping an unnecessary call
tool: "poni -E" for passing exceptions thru from the main function
core: minor refactoring