Fix #61094 Wrong WSDL cache file name

WSDL cache files are created with the format wsdl-owner_username-uri_md5sum and with permission 0600. This has resulted in an error when two or more users are trying to run the same script that uses the same wsdl: only the first user can access to the wsdl cache file, while a second user will encounter a SOAP-ERROR complaining about not being about to load the WSDL. The bug was introduced in commit 1a9e668a04 which was supposed to use getuid() instead of php_get_current_user() in the cache filename. 

To reproduce the problem, use the following code and run the script with two different users:
   
    <?php
    $client = new SoapClient('http://www.webservicex.net/stockquote.asmx?WSDL');

The second user (non-root) would see this error:

    PHP Fatal error:  SOAP-ERROR: Parsing WSDL: Couldn't load from 'http://www.webservicex.net/stockquote.asmx?WSDL' : failed to load external entity "http://www.webservicex.net/stockquote.asmx?WSDL"

[Bug #51407](https://bugs.php.net/bug.php?id=51407) also describes the same problem.

Please take a look at it. Thanks.