osc_ucx: add worker flush before osc module free

Make sure all pending communications are done on all ranks before
closing the window. This way it will be safe to close the endpoints when
closing the component.

(picked from master b8e1af6)

Signed-off-by: Yossi Itigin <yosefe@mellanox.com>

ompi/mca/osc/ucx/osc_ucx_component.c

@@ -804,6 +804,8 @@ int ompi_osc_ucx_free(struct ompi_win_t *win) {
         ucp_worker_progress(mca_osc_ucx_component.ucp_worker);
     }
 
+    opal_common_ucx_worker_flush(mca_osc_ucx_component.ucp_worker);
+
     ret = module->comm->c_coll->coll_barrier(module->comm,
                                              module->comm->c_coll->coll_barrier_module);