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_start_server.inc

@@ -0,0 +1,54 @@
+# ==== Purpose ====
+#
+# Start the server given by $rpl_server_number.  This should normally
+# be invoked after rpl_stop_server.inc.
+#
+# ==== Usage ====
+#
+# --let $rpl_server_number= N
+# [--let $rpl_server_parameters= --flag1 --flag2 ...]
+# [--let $rpl_debug= 1]
+# --source include/rpl_start_server.inc
+#
+# Parameters:
+#
+#   $rpl_server_number
+#     Number to identify the server that needs to reconnect.  1 is the
+#     master server, 2 the slave server, 3 the 3rd server, and so on.
+#     Cf. include/rpl_init.inc
+#
+#   $rpl_server_parameters
+#     If set, extra parameters given by this variable are passed to
+#     mysqld.
+#
+#   $rpl_debug
+#     See include/rpl_init.inc
+#
+# ==== See also ====
+#
+# rpl_stop_server.inc
+# rpl_restart_server.inc
+
+
+--let $_rpl_start_server_command= restart
+--let $_rpl_start_server_args= [server_number=$rpl_server_number]
+if ($rpl_server_parameters)
+{
+  --let $_rpl_start_server_command= restart:$rpl_server_parameters
+  --let $_rpl_start_server_args= [server_number=$rpl_server_number parameters: $rpl_server_parameters]
+}
+
+--let $include_filename= rpl_start_server.inc $_rpl_start_server_args
+--source include/begin_include_file.inc
+
+--let $rpl_connection_name= server_$rpl_server_number
+--source include/rpl_connection.inc
+
+# Write file to make mysql-test-run.pl start up the server again
+--exec echo "$_rpl_start_server_command" > $MYSQLTEST_VARDIR/tmp/mysqld.$rpl_server_number.expect
+
+--source include/rpl_reconnect.inc
+
+
+--let $include_filename= rpl_start_server.inc $_rpl_start_server_args
+--source include/end_include_file.inc