BUG#49978: Replication tests don't clean up replication state at the end

Major replication test framework cleanup. This does the following:
 - Ensure that all tests clean up the replication state when they
   finish, by making check-testcase check the output of SHOW SLAVE STATUS.
   This implies:
    - Slave must not be running after test finished. This is good
      because it removes the risk for sporadic errors in subsequent
      tests when a test forgets to sync correctly.
    - Slave SQL and IO errors must be cleared when test ends. This is
      good because we will notice if a test gets an unexpected error in
      the slave threads near the end.
    - We no longer have to clean up before a test starts.
 - Ensure that all tests that wait for an error in one of the slave
   threads waits for a specific error. It is no longer possible to
   source wait_for_slave_[sql|io]_to_stop.inc when there is an error
   in one of the slave threads. This is good because:
    - If a test expects an error but there is a bug that causes
      another error to happen, or if it stops the slave thread without
      an error, then we will notice.
    - When developing tests, wait_for_*_to_[start|stop].inc will fail
      immediately if there is an error in the relevant slave thread.
      Before this patch, we had to wait for the timeout.
 - Remove duplicated and repeated code for setting up unusual replication
   topologies. Now, there is a single file that is capable of setting
   up arbitrary topologies (include/rpl_init.inc, but
   include/master-slave.inc is still available for the most common
   topology). Tests can now end with include/rpl_end.inc, which will clean
   up correctly no matter what topology is used. The topology can be
   changed with include/rpl_change_topology.inc.
 - Improved debug information when tests fail. This includes:
    - debug info is printed on all servers configured by include/rpl_init.inc
    - User can set $rpl_debug=1, which makes auxiliary replication files
      print relevant debug info.
 - Improved documentation for all auxiliary replication files. Now they
   describe purpose, usage, parameters, and side effects.
 - Many small code cleanups:
    - Made have_innodb.inc output a sensible error message.
    - Moved contents of rpl000017-slave.sh into rpl000017.test
    - Added mysqltest variables that expose the current state of
      disable_warnings/enable_warnings and friends.
    - Too many to list here: see per-file comments for details.

mysql-test/include/rpl_end.inc

@@ -0,0 +1,103 @@
+# ==== Purpose ====
+#
+# Shut down replication initialized by include/rpl_init.inc.
+#
+# This syncs all servers, executes STOP SLAVE on all servers, executes
+# CHANGE MASTER on all servers, and disconnects all connections
+# configured by rpl_init.inc.
+#
+# It does not execute RESET MASTER or RESET SLAVE, because that would
+# remove binlogs which are possibly useful debug information in case
+# the test case later fails with a result mismatch.  If you need that,
+# source include/rpl_reset.inc before you source this file.
+#
+#
+# ==== Usage ====
+#
+# [--let $rpl_only_running_threads= 1]
+# [--let $rpl_debug= 1]
+# --source include/rpl_end.inc
+#
+# Parameters:
+#   $rpl_only_running_threads
+#     If one or both of the IO and SQL threads is stopped, sync and
+#     stop only the threads that are running.  See
+#     include/rpl_sync.inc and include/stop_slave.inc for details.
+#
+#   $rpl_debug
+#     See include/rpl_init.inc
+#
+# Note:
+#   This script will fail if Last_SQL_Error or Last_IO_Error is
+#   nonempty.  If you expect an error in the SQL thread, you should
+#   normally call this script as follows:
+#
+#     --source include/wait_for_slave_sql_error.inc
+#     --source include/stop_slave_io.inc
+#     RESET SLAVE;
+#     --let $rpl_only_running_threads= 1
+#     --source include/rpl_end.inc
+#
+#
+# ==== Side effects ====
+#
+# Changes the current connection to 'default'.
+
+
+--let $include_filename= rpl_end.inc
+--source include/begin_include_file.inc
+
+
+if (!$rpl_inited)
+{
+  --die ERROR IN TEST: rpl_end.inc was sourced when replication was not configured. Most likely, rpl_end.inc was sourced twice or rpl_init.inc has not been sourced.
+}
+
+
+if ($rpl_debug)
+{
+  --echo ---- Check that no slave thread has an error ----
+}
+
+--let $_rpl_server= $rpl_server_count
+while ($_rpl_server)
+{
+  --let $rpl_connection_name= server_$_rpl_server
+  --source include/rpl_connection.inc
+
+  # Only check slave threads for error on hosts that were at some
+  # point configured as slave.
+  --let $_tmp= query_get_value(SHOW SLAVE STATUS, Master_Host, 1)
+  if (`SELECT '$_tmp' != 'No such row'`)
+  {
+    --source include/check_slave_no_error.inc
+  }
+
+  --dec $_rpl_server
+}
+
+--source include/rpl_sync.inc
+--source include/rpl_stop_slaves.inc
+
+# mtr configures server 2 to be a slave before it runs the test. We
+# have to restore that state now, so we change topology to 1->2.
+--let $rpl_topology= 1->2
+--source include/rpl_change_topology.inc
+
+
+--connection default
+--let $_rpl_server= $rpl_server_count
+--let $_rpl_one= _1
+while ($_rpl_server)
+{
+  --disconnect server_$_rpl_server
+  --disconnect server_$_rpl_server$_rpl_one
+  --dec $_rpl_server
+}
+
+--let $rpl_inited= 0
+
+# Do not restore connection, because we have disconnected it.
+--let $skip_restore_connection= 1
+--let $include_filename= rpl_end.inc
+--source include/end_include_file.inc