Passing potentially arbitrary data into a shellscript is potentially
very broken if you do not correctly quote it for use. This quoting must
be done as part of the interpretation of the data itself, e.g. python's
shlex.quote; simply formatting it into a string with double quotes is
NOT sufficient.
An alternative is to communicate the data reliably via argv to the shell
process, and allow the shell to internally handle it via `"$1"`, which
is quote-safe and will expand the data from argv as a single tokenized
word.
This fixes a minor bug introduced by 10af8bb24b.
Before the commit, the interface group was set only when Group= is explicitly
specified, otherwise the interface group was kept. However, after the commit,
we need to specify Group= with an empty string to keep the current interface
group.
let's not make up new errors in these checks that validate if connect()
work at all. After all, we don't really know if the ENXIO we saw earlier
actually is really caused by the inode being an AF_UNIX socket, we just
have the suspicion...
This way we can implement nice fallbacks later on.
While we are at it, provide a test for this (one that is a bit over the
top, but then again, we can never have enough tests).
