More throughout logging in PythonSdkUpdater

Add cause to the logged exception so that it's possible to see where
exactly SDK updating process was launched which is impossible at the
moment because of the nested backgroundable task and invokeLater().

python/src/com/jetbrains/python/sdk/PythonSdkUpdater.java

@@ -133,6 +133,7 @@ public class PythonSdkUpdater implements StartupActivity {
       return true;
     }
 
+    @SuppressWarnings("ThrowableInstanceNeverThrown") final Throwable methodCallStacktrace = new Throwable();
     application.invokeLater(() -> {
       synchronized (ourLock) {
         if (!ourScheduledToRefresh.contains(homePath)) {
@@ -165,6 +166,7 @@ public class PythonSdkUpdater implements StartupActivity {
                   PyPackageManager.getInstance(sdk12).refreshAndGetPackages(true);
                 }
                 catch (ExecutionException e) {
+                  e.initCause(methodCallStacktrace);
                   LOG.warn(e);
                 }
               }