MDEV-8345 STOP SLAVE should not cause an ERROR to be logged to the error log

cherry-pick from 5.7:
  commit 6b24763
  Author: Manish Kumar <manish.4.kumar@oracle.com>
  Date:   Tue Mar 27 13:10:42 2012 +0530

  BUG#12977988 - ON STOP SLAVE: ERROR READING PACKET FROM SERVER: LOST CONNECTION
                 TO MYSQL SERVER
  BUG#11761457 - ERROR 2013 + "ERROR READING RELAY LOG EVENT" ON STOP SLAVEBUG#12977988 - ON STOP SLAVE: ERROR READING PACKET FROM SERVER: LOST CONNECTION
               TO MYSQL SERVER

mysql-test/suite/rpl/r/rpl_stop_slave_error.result

+include/master-slave.inc
+[connection master]
+include/stop_slave.inc
+NOT FOUND /Error reading packet from server: Lost connection/ in slave_log.err
+include/start_slave.inc
+include/rpl_end.inc

mysql-test/suite/rpl/t/rpl_stop_slave_error-slave.opt

+--log-error=$MYSQLTEST_VARDIR/tmp/slave_log.err

mysql-test/suite/rpl/t/rpl_stop_slave_error.test

+#
+# MDEV-8345 STOP SLAVE should not cause an ERROR to be logged to the error log
+#
+source include/have_binlog_format_mixed.inc; # don't repeat the test three times
+source include/master-slave.inc;
+
+connection master;
+sync_slave_with_master;
+source include/stop_slave.inc;
+let SEARCH_FILE=$MYSQLTEST_VARDIR/tmp/slave_log.err;
+let SEARCH_PATTERN=Error reading packet from server: Lost connection;
+let SEARCH_RANGE= -50000;
+source include/search_pattern_in_file.inc;
+
+source include/start_slave.inc;
+source include/rpl_end.inc;
+

sql/slave.cc

@@ -3120,8 +3120,13 @@ static ulong read_event(MYSQL* mysql, Master_info *mi, bool* suppress_warnings)
       *suppress_warnings= TRUE;
     }
     else
-      sql_print_error("Error reading packet from server: %s ( server_errno=%d)",
-                      mysql_error(mysql), mysql_errno(mysql));
+    {
+      if (!mi->rli.abort_slave)
+      {
+        sql_print_error("Error reading packet from server: %s (server_errno=%d)",
+                        mysql_error(mysql), mysql_errno(mysql));
+      }
+    }
     DBUG_RETURN(packet_error);
   }