Fix ctkColorDialogTest2 time out

ctkColorDialog::getColor() already pops up the dialog, there is no need to
exec the app. It would otherwise hang there as no window is shown.
Remove ctkColorDialog warnings when not using nameSignal

If not provided, the nameSignal property is const char* 0. It is a valid
QVariant, but it can't be used to connect/disconnect.
Merge branch 'ctkcolordialogtest2-timeout'

* ctkcolordialogtest2-timeout:
  Remove ctkColorDialog warnings when not using nameSignal
  Fix ctkColorDialogTest2 time out