Canceling git clone does not terminate the process(es)

Steps to reproduce:

• trigger "New Project.." > "Import Project" > "Git Clone"
• use a repository that doesn't finish fast when cloning (e.g. QC)
• when the cloning starts use the Cancel button
• the clone stops (or at least it appears so, as no more output is printed and clone failed is printed)

• head over to the directory you've cloned into and watch as it is still getting populated more and more
• or verify with taskmgr or processexplorer that processes like "git clone", "git index-pack" are still running
• closing QC now will also not fully terminate QC until all git processes have finished (processlauncher never finishes, so QC does not really finish even after closing QC)
  (you don't really notice this, as QC's window is no more present, but looking into taskmgr QC and qtcreator_processlauncher are running even after the inner git processes have finished)

On Linux, canceling git clone task leaves this process as a zombie (it's left also after creator quits):

/usr/bin/ssh -o SendEnv=GIT_PROTOCOL -p 29418 jkobus@codereview.qt-project.org git-upload-pack '/qt-creator/qt-creator'