fs-util,test: add helper to remove tempfiles

This simplifies the use of tempfiles in tests and fixes "leaked"
temporary files in test-fileio, test-catalog, test-conf-parser.

Not the whole tree is converted.

src/basic/fs-util.c

@@ -1066,6 +1066,15 @@ int access_fd(int fd, int mode) {
         return r;
 }
 
+void unlink_tempfilep(char (*p)[]) {
+        /* If the file is created with mkstemp(), it will (almost always)
+         * change the suffix. Treat this as a sign that the file was
+         * successfully created. We ignore both the rare case where the
+         * original suffix is used and unlink failures. */
+        if (!endswith(*p, ".XXXXXX"))
+                (void) unlink(*p);
+}
+
 int unlinkat_deallocate(int fd, const char *name, int flags) {
         _cleanup_close_ int truncate_fd = -1;
         struct stat st;

src/basic/fs-util.h

@@ -104,6 +104,7 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(char*, unlink_and_free);
 
 int access_fd(int fd, int mode);
 
+void unlink_tempfilep(char (*p)[]);
 int unlinkat_deallocate(int fd, const char *name, int flags);
 
 int fsync_directory_of_file(int fd);