pml/ob1: add missing ompi_request_wait_completion for buffered sends

This commit adds a call to ompi_request_wait_completion for buffered
sends. Without this line it is possible to get into a state where the
data is never sent.

Fixes open-mpi/ompi#1185

Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>

ompi/mca/pml/ob1/pml_ob1_isend.c

@@ -198,7 +198,7 @@ int mca_pml_ob1_send(const void *buf,
             return rc;
         }
 
-        /* free the request and return. don't care if it completes now */
+        ompi_request_wait_completion (brequest);
         ompi_request_free (&brequest);
         return OMPI_SUCCESS;
     }