tmpfiles: make sure "C" doesn't copy anything if the destination already exists

Previously it would recursively copy the entire tree in, and descend
into subdirectories even if the destination already exists. Let's do
what the documentation says and not do that.

If files down the tree shall be copied too, they should get their own
"C" lines.
diff --git a/src/tmpfiles/tmpfiles.c b/src/tmpfiles/tmpfiles.c
index c6c8ce8..cbad78a 100644
--- a/src/tmpfiles/tmpfiles.c
+++ b/src/tmpfiles/tmpfiles.c
@@ -667,10 +667,29 @@
                 break;
 
         case COPY_FILES:
-                r = copy_tree(i->argument, i->path);
+                r = copy_tree(i->argument, i->path, false);
                 if (r < 0) {
-                        log_error("Failed to copy files to %s: %s", i->path, strerror(-r));
-                        return r;
+                        struct stat a, b;
+
+                        if (r != -EEXIST) {
+                                log_error("Failed to copy files to %s: %s", i->path, strerror(-r));
+                                return -r;
+                        }
+
+                        if (stat(i->argument, &a) < 0) {
+                                log_error("stat(%s) failed: %m", i->argument);
+                                return -errno;
+                        }
+
+                        if (stat(i->path, &b) < 0) {
+                                log_error("stat(%s) failed: %m", i->path);
+                                return -errno;
+                        }
+
+                        if ((a.st_mode ^ b.st_mode) & S_IFMT) {
+                                log_debug("Can't copy to %s, file exists already and is of different type", i->path);
+                                return 0;
+                        }
                 }
 
                 r = item_set_perms(i, i->path);
@@ -694,19 +713,21 @@
                         r = mkdir_label(i->path, i->mode);
                 }
 
-                if (r < 0 && r != -EEXIST) {
-                        log_error("Failed to create directory %s: %s", i->path, strerror(-r));
-                        return r;
-                }
+                if (r < 0) {
+                        if (r != -EEXIST) {
+                                log_error("Failed to create directory %s: %s", i->path, strerror(-r));
+                                return r;
+                        }
 
-                if (stat(i->path, &st) < 0) {
-                        log_error("stat(%s) failed: %m", i->path);
-                        return -errno;
-                }
+                        if (stat(i->path, &st) < 0) {
+                                log_error("stat(%s) failed: %m", i->path);
+                                return -errno;
+                        }
 
-                if (!S_ISDIR(st.st_mode)) {
-                        log_error("%s is not a directory.", i->path);
-                        return -EEXIST;
+                        if (!S_ISDIR(st.st_mode)) {
+                                log_debug("%s already exists and is not a directory.", i->path);
+                                return 0;
+                        }
                 }
 
                 r = item_set_perms(i, i->path);