ClangTools: Fix clazy output parsing

We must not paste stdout and stderr together, because if there is stderr
output (as in some versions of clazy), then the trailing messages will
make the JSON parsing fail.

Change-Id: Ia31efdf3376eeb2e232b32bb0cdb543345e2dbfc
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/clangtools/executableinfo.cpp

@@ -64,7 +64,7 @@ static QString runExecutable(const Utils::CommandLine &commandLine,
         return {};
     }
 
-    return response.allOutput();
+    return response.stdOut();
 }
 
 static QStringList queryClangTidyChecks(const QString &executable,