The reexec package facilitates the busybox style reexec of the docker binary that we require because
of the forking limitations of using Go. Handlers can be registered with a name and the argv 0 of
the exec of the binary will be used to find and execute custom init paths.
Command returns *exec.Cmd which has Path as current binary. Also it setting
SysProcAttr.Pdeathsig to SIGTERM.
This will use the in-memory version (/proc/self/exe) of the current binary,
it is thus safe to delete or replace the on-disk binary (os.Args[0]).