libsystemd: new library, refactor sd-daemon.[ch] test code

This commit introduces a bare-bones replacement for libsystemd:

 - Build .so file and add --with-libsystemd to configure
 - Add capabilities support to test/src/serv.c
 - Update tests to account for a Finit built w/o libsystemd support

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

test/notify.sh

@@ -25,6 +25,15 @@ test_one()
     type=$1
     service=$2
 
+    # Skip systemd tests if serv doesn't have libsystemd support
+    if [ "$type" = "systemd" ]; then
+        if ! "$TEST_DIR/src/serv" -C | grep -q "libsystemd"; then
+	    sep
+            say "Skipping systemd test - serv built without libsystemd support"
+            return 0
+        fi
+    fi
+
     sep
 
 #    num=$(run "find /proc/1/fd |wc -l")