rpl_percona_bug1070255 may crash due to concurrent dbug access

On 5.5 trunk:

rpl.rpl_percona_bug1070255 'row' w1 [ fail ]
...
mysqltest: In included file "./include/rpl_end.inc":
included from ./include/rpl_end.inc at line 77:
At line 77: query 'let $_tmp= query_get_value(SHOW SLAVE STATUS, Master_Host, 1)' failed: 2013: Lost connection to MySQL server during query
...
Program terminated with signal SIGSEGV, Segmentation fault.
#0 __pthread_kill (threadid=<optimized out>, signo=signo@entry=11) at ../sysdeps/unix/sysv/linux/pthread_kill.c:62
62 ../sysdeps/unix/sysv/linux/pthread_kill.c: No such file or directory.
[Current thread is 1 (Thread 0x7f622440b700 (LWP 23374))]
#0 __pthread_kill (threadid=<optimized out>, signo=signo@entry=11) at ../sysdeps/unix/sysv/linux/pthread_kill.c:62
#1 0x0000000000805ff7 in my_write_core (sig=sig@entry=11) at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/mysys/stacktrace.c:433
#2 0x00000000006c3a15 in handle_fatal_signal (sig=11) at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/sql/signal_handler.cc:250
#3 <signal handler called>
#4 internal_fnmatch (pattern=<optimized out>, string=string@entry=0xae07d0 "warning", string_end=0xae07d7 "", no_leading_period=no_leading_period@entry=0, flags=flags@entry=0, ends=ends@entry=0x0, alloca_used=0) at fnmatch_loop.c:62
#5 0x00007f6228b7d24d in __fnmatch (pattern=pattern@entry=0x616e5f6c71737976 <error: Cannot access memory at address 0x616e5f6c71737976>, string=string@entry=0xae07d0 "warning", flags=flags@entry=0) at fnmatch.c:458
#6 0x0000000000a7cf3c in InList (linkp=0x616e5f6c7173796d, cp=cp@entry=0xae07d0 "warning") at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/dbug/dbug.c:1501
#7 0x0000000000a7e3dc in _db_keyword_ (cs=cs@entry=0x7f61f8016c80, keyword=0xae07d0 "warning", strict=65538, strict@entry=0) at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/dbug/dbug.c:1718
#8 0x0000000000a7e4b9 in _db_doprnt_ (format=format@entry=0xb63ff0 "Read only %d bytes off %lu from %d, errno: %d") at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/dbug/dbug.c:1262
#9 0x000000000080231a in my_read (Filedes=Filedes@entry=58, Buffer=Buffer@entry=0x7f61f8007e30 "N\250\227W\002\001", Count=Count@entry=5805, MyFlags=MyFlags@entry=16) at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/mysys/my_read.c:66
#10 0x00000000007eac9d in inline_mysql_file_read (flags=16, count=5805, buffer=0x7f61f8007e30 "N\250\227W\002\001", file=58, src_line=563, src_file=0xb5edb8 "/mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/mysys/mf_iocache.c") at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/include/mysql/psi/mysql_file.h:1144
#11 _my_b_read (info=0x7f6224409a10, Buffer=0x7f6224409830 "@\230@$b\177", Count=19) at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/mysys/mf_iocache.c:562
#12 0x000000000076b37c in Log_event::read_log_event (file=file@entry=0x7f6224409a10, packet=packet@entry=0x3955910, log_lock=log_lock@entry=0x11af608 <mysql_bin_log+8>, log_file_name_arg=log_file_name_arg@entry=0x7f6224409b70 "./master-bin.000001", is_binlog_active=is_binlog_active@entry=0x7f622440997f) at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/sql/log_event.cc:1049
#13 0x00000000005b9eaf in mysql_binlog_send (thd=thd@entry=0x3955280, log_ident=0x7f61f8004b00 "master-bin.000001", pos=<optimized out>, pos@entry=4, flags=flags@entry=0) at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/sql/sql_repl.cc:683
#14 0x00000000005a28fb in dispatch_command (command=command@entry=COM_BINLOG_DUMP, thd=thd@entry=0x3955280, packet=packet@entry=0x39673d1 "", packet_length=packet_length@entry=27) at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/sql/sql_parse.cc:1272
#15 0x00000000005a3c22 in do_command (thd=0x3955280) at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/sql/sql_parse.cc:789
#16 0x00000000006585a1 in do_handle_one_connection (thd_arg=thd_arg@entry=0x3955280) at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/sql/sql_connect.cc:1418
#17 0x000000000065869e in handle_one_connection (arg=arg@entry=0x3955280) at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/sql/sql_connect.cc:1325
#18 0x00000000008289e6 in pfs_spawn_thread (arg=0x393db90) at /mnt/workspace/percona-server-5.5-trunk/BUILD_TYPE/debug/Host/ubuntu-wily-64bit/storage/perfschema/pfs.cc:1015
#19 0x00007f6229fed6aa in start_thread (arg=0x7f622440b700) at pthread_create.c:333
#20 0x00007f6228bb013d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

The --source include/rpl_stop.inc is preceded by set global DEBUG=''; executed with the slaves running. Thus, this has the same underlying issue as upstream bug 58754 / 11765758 and should be addressed the same - by not executing SET GLOBAL DEBUG=... while slaves are running