use private linkage where appropriate

Task-number: QTBUG-35781
Change-Id: I24b5ec010525da2c1f1be63996193ac31dcd3808
Reviewed-by: Laszlo Papp <lpapp@kde.org>
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>
Add the minimal set of the base auto tests

Added two types of tests: the constructing tests and the opening tests.

The construction tests are checking of the getters to return of default values.
Also are checking a correctness work of the constructor of class with different
types of a port name.

The opening tests are checking the open() method with the valid/invalid open
modes and with the valid/invalid port names. The results are compared with the
expected behavior (with the error codes and the return values).

Change-Id: I503adf629cf613844bf9b96d8704ff017ea5fcdb
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
Merge remote-tracking branch 'origin/stable' into dev

Change-Id: I6b339cfcfcc8cebab09991b634076bc854229e28