xgetcwd is used only in a test, so there is no need to pull a gnulib
module just for it.
Switch to use getcwd directly with a fixed buffer: the tests would have
failed with paths longer than 992 characters, as the libvirt_uri would
have been truncated. Since there were no reports of issues, we can
assume that the current working directory will fit in 1024 characters;
adapt the size of libvirt_uri accordingly.
a2b37a495c