Some of the tests fails when running unit tests behind proxy.

1. Error in PMA_Util_Test::testGetLatestVersion

2. Failure in PMA_ConfigTest::testCheckHTTP

The error (1) can be surely avoided if ProxyUrl is properly set. I still trying to figure out the exact cause of failure, but looks like it is related to proxy settings.

I could not see example of how to set cfg in `bootstrap.php` for tests. Also, some of the tests overrides ProxyUrl cfg variable. Any workaround?

Also, how about setting default value of config variable from environmental variable like http_proxy or similar whenever available in PMA?

Thanks.
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