fix AppTestSocket.().test_invalid_fd

Merged Bitbucket Importer requested to merge bitbucket/merged-pr-650 into branch/py3.6

Created originally on Bitbucket by csernazs (Zsolt Cserna)

Was already merged in Bitbucket before import, marked as merged by the import user

Rename the kwarg from fdobj to fileno. fdobj comes from the C implementation of _socket in cpython but the test specifies it by keyword so it needs to be changed accordingly.

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