Create lockfile parent dir

[SWW13]

When ifupdown2 is run it tries to open the lockfile (default: /run/network/.lock), if that fails the error Another instance of this program is already running is printed.

However, this also happens when the parent directory (/run/network) doesn't exist. It would be nice to automatically try to create parent dirs, if they are missing, or at least alter the error message in this case.
This behavior currently prevents debian to install ifupdown2 as part of a preseed config (installation automation) due to the missing /run/network dir.