nspawn: optionally run a stub init process as PID 1 This adds a new switch --as-pid2, which allows running commands as PID 2, while a stub init process is run as PID 1. This is useful in order to run arbitrary commands in a container, as PID1's semantics are different from all other processes regarding reaping of unknown children or signal handling.

nspawn: add new --chdir= switch Fixes: #2192

nspawn: add new --network-veth-extra= switch for defining additional veth links The new switch operates like --network-veth, but may be specified multiple times (to define multiple link pairs) and allows flexible definition of the interface names. This is an independent reimplementation of #1678, but defines different semantics, keeping the behaviour completely independent of --network-veth. It also comes will full hook-up for .nspawn files, and the matching documentation.

nspawn: add missing comma to gperf file

nspawn: remove nspawn.h, it's empty now

nspawn: split all port exposure code into nspawn-expose-port.[ch]

nspawn: add new .nspawn files for container settings .nspawn fiels are simple settings files that may accompany container images and directories and contain settings otherwise passed on the nspawn command line. This provides an efficient way to attach execution data directly to containers.