CppTools: Cleanup completion tests #2

Change-Id: I3c5f42de464a5607f1caa6a48d881c5a4a113ec3
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>
CppTools: Generalize data-driven test_completion

Change-Id: I409a00b869a95dff2d69c9744da75c324c82776a
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>