dbus-daemon test: Don't test fd limits if in an unprivileged container
In an unprivileged container, uid 0 doesn't have CAP_SYS_RESOURCE, so we can't expect the dbus-daemon to be able to escalate its fd limit.
This can be reproduced using bubblewrap:
sudo bwrap \
--cap-drop CAP_SYS_RESOURCE \
--ro-bind / / \
--dev /dev \
env \
DBUS_TEST_DAEMON=.../bus/dbus-daemon \
DBUS_TEST_DATA=.../test/data \
.../test/test-dbus-daemon \
-p /fd-limit \
--verbose
Bug-Debian: https://bugs.debian.org/908092