empty request headers and body in *.log files when using log_dir option

[ingvarbiz]

In base.py, function save_dumps():
out.write(b'Request headers:\n')
out.write(self.request_head)
out.write(b'\n')
out.write(b'Request body:\n')
out.write(self.request_body)

Both self.request_head and self.request_body are equal empty string (b'') all the time.

*.log files contain response data only.