Avoid code duplication in TestBlackboxBase::runQbs
Avoid code duplication in TestBlackboxBase::runQbs

Now we write log in both success and error cases, the only difference is
that we reset exitCode to -1 in error case.

Change-Id: I2ffe9b14c0ba1ad11acd9f81f35a0594dda26c12
Reviewed-by: Christian Kandeler <3aa99dcdd3f0cac61fb81c2a11771c0cc2497607@qt.io>

qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs