Qbs: Clear build system related tasks before reparsing qbs
Qbs: Clear build system related tasks before reparsing qbs

Task-number: QTCREATORBUG-9778

Change-Id: Ic054f1619832a5ff0ea53d7fc5225fe674ddac13
Reviewed-by: Tobias Hunger <012f8d714267bccc9d4766fbeace9f175fcc70c4@digia.com>

colede/qtcreator,danimo/qt-creator,xianian/qt-creator,amyvmiwei/qt-creator,darksylinc/qt-creator,omniacreator/qtcreator,malikcjm/qtcreator,danimo/qt-creator,malikcjm/qtcreator,colede/qtcreator,darksylinc/qt-creator,kuba1/qtcreator,martyone/sailfish-qtcreator,richardmg/qtcreator,kuba1/qtcreator,maui-packages/qt-creator,xianian/qt-creator,martyone/sailfish-qtcreator,AltarBeastiful/qt-creator,maui-packages/qt-creator,danimo/qt-creator,amyvmiwei/qt-creator,AltarBeastiful/qt-creator,AltarBeastiful/qt-creator,malikcjm/qtcreator,omniacreator/qtcreator,darksylinc/qt-creator,AltarBeastiful/qt-creator,danimo/qt-creator,amyvmiwei/qt-creator,xianian/qt-creator,amyvmiwei/qt-creator,amyvmiwei/qt-creator,danimo/qt-creator,Distrotech/qtcreator,darksylinc/qt-creator,martyone/sailfish-qtcreator,Distrotech/qtcreator,xianian/qt-creator,Distrotech/qtcreator,martyone/sailfish-qtcreator,richardmg/qtcreator,colede/qtcreator,farseerri/git_code,farseerri/git_code,maui-packages/qt-creator,richardmg/qtcreator,Distrotech/qtcreator,amyvmiwei/qt-creator,omniacreator/qtcreator,farseerri/git_code,xianian/qt-creator,maui-packages/qt-creator,richardmg/qtcreator,farseerri/git_code,richardmg/qtcreator,Distrotech/qtcreator,kuba1/qtcreator,richardmg/qtcreator,martyone/sailfish-qtcreator,colede/qtcreator,kuba1/qtcreator,kuba1/qtcreator,omniacreator/qtcreator,farseerri/git_code,kuba1/qtcreator,maui-packages/qt-creator,farseerri/git_code,martyone/sailfish-qtcreator,Distrotech/qtcreator,omniacreator/qtcreator,martyone/sailfish-qtcreator,xianian/qt-creator,darksylinc/qt-creator,colede/qtcreator,malikcjm/qtcreator,malikcjm/qtcreator,martyone/sailfish-qtcreator,amyvmiwei/qt-creator,malikcjm/qtcreator,amyvmiwei/qt-creator,colede/qtcreator,richardmg/qtcreator,colede/qtcreator,darksylinc/qt-creator,kuba1/qtcreator,xianian/qt-creator,xianian/qt-creator,AltarBeastiful/qt-creator,Distrotech/qtcreator,kuba1/qtcreator,omniacreator/qtcreator,danimo/qt-creator,farseerri/git_code,AltarBeastiful/qt-creator,omniacreator/qtcreator,danimo/qt-creator,darksylinc/qt-creator,martyone/sailfish-qtcreator,maui-packages/qt-creator,danimo/qt-creator,AltarBeastiful/qt-creator,farseerri/git_code,xianian/qt-creator,malikcjm/qtcreator,darksylinc/qt-creator,maui-packages/qt-creator,danimo/qt-creator,AltarBeastiful/qt-creator,kuba1/qtcreator