Fix rest module to reset request variables in the before hook

The rest module is not resetting the headers on each test, thus carrying the same headers all over the test suite. This PR fixes that, resetting the server parameters of the client on each test.
Yes, it is being used as u can see here https://github.com/brutuscat/Codeception/blob/5dc96fa72011b7eebf8792c7d5989c9da8c62532/src/Codeception/Module/REST.php#L359 But the contents of `$headers` is copied into the client server paramerters  upon request execution as shown in the link.