nspawn: add /dev FD symlinks in container setup

This creates /dev/fd, /dev/stdin, /dev/stdout, /dev/stderr, and
/dev/core as symlinks to /proc on container creation. Except for
/dev/core, these are needed for shells like bash to be fully functional.

src/nspawn/nspawn.c

@@ -53,6 +53,7 @@
 #include "path-util.h"
 #include "loopback-setup.h"
 #include "sd-id128.h"
+#include "dev-setup.h"
 
 typedef enum LinkJournal {
         LINK_NO,
@@ -1204,6 +1205,8 @@ int main(int argc, char *argv[]) {
                 if (copy_devnodes(arg_directory) < 0)
                         goto child_fail;
 
+                dev_setup(arg_directory);
+
                 if (setup_dev_console(arg_directory, console) < 0)
                         goto child_fail;