PythonHelper: Add support for bool.

Convert Python bool type from/to C++/QVariant bool (QVariant::Bool) in
PythonHelper::variantToPyObject and PythonHelper::variantFromPyObject.

This fixes the "override" option and any booleans in the "defaults" list
in grubcfg.conf.

src/libcalamares/PythonHelper.cpp

@@ -53,6 +53,9 @@ variantToPyObject( const QVariant& variant )
     case QVariant::String:
         return bp::object( variant.toString().toStdString() );
 
+    case QVariant::Bool:
+        return bp::object( variant.toBool() );
+
     default:
         return bp::object();
     }
@@ -78,6 +81,9 @@ variantFromPyObject( const boost::python::object& pyObject )
     else if ( pyType == "str" )
         return QVariant( QString::fromStdString( bp::extract< std::string >( pyObject ) ) );
 
+    else if ( pyType == "bool" )
+        return QVariant( bp::extract< bool >( pyObject ) );
+
     else
         return QVariant();
 }