First and foremost: use ephemeral (/run, $XDG) directories
for systemd unit files, so as not to vandalize a working system.
Second, refactor common systemd-related functionality into
a new helper file, loaded by the systemd-related tests.
Shared functionality includes:
* setting $XDG_RUNTIME_DIR if unset and rootless
* setting $UNIT_DIR for use by tests
* new systemctl() and journalctl() functions, which
include "--user" when rootless (why can't systemd
figure this out on its own?)
Signed-off-by: Ed Santiago <santiago@redhat.com>
