t/fiotestlib: make recorded command prettier

Instead of recording fio test commands as a single very long line, put
each option on its own line to make the command easier for humans to
digest.

Signed-off-by: Vincent Fu <vincent.fu@samsung.com>

t/fiotestlib.py

@@ -75,7 +75,7 @@ def run(self):
         command = [self.paths['exe']] + self.parameters
         with open(self.filenames['cmd'], "w+",
                   encoding=locale.getpreferredencoding()) as command_file:
-            command_file.write(" ".join(command))
+            command_file.write(" \\\n ".join(command))
 
         try:
             with open(self.filenames['stdout'], "w+",