shell-completion: prevent mangling unit names

Units with literal hex '\xFF' in their names has to be read
and printed properly.
dev-disk-byx2dlabel-root.device != dev-disk-by\x2dlabel-root.device
Always check asprintf return code

There is a small number of the places in sources where we don't check
asprintf() return code and assume that after error the function
returns NULL pointer via the first argument. That's wrong, after
error the content of pointer is undefined.
analyze: fix seg-fault with no cl-argument

We need to check if argv[1] is set before compare
systemctl: do not bother to mutate state on error

We will abort anyway.
Add utility function to append root to path
update-done: include a short description in .updated

People might be confused where the file comes from, since the name is not
at all specific.

https://bugzilla.redhat.com/show_bug.cgi?id=1121301#c8
Print kdbus path when opening fails

This makes it easier to debug what is going on.