QtIFW

Make Virtual and Default tag mutually exclusive.

Call m_vars value function directly.
1; To prevent recursive calls in case of key "Default".
2; To avoid the extra function call to fetch values from m_vars in
   case of other values set in the object.

Change-Id: I8f40b53704d1f314071d7060d0c92829310c262d
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>
Reviewed-by: Niels Weber <niels.weber@digia.com>