``pt-online-schema-change`` was not recognizing the slave with multi-source replication active.

$ pt-online-schema-change --socket=/tmp/mysql_sandbox45007.sock --user msandbox --password msandbox --execute \
> --alter "ADD placeOfServiceCategor1121 BIGINT(19)" D=test,t=joinit --alter-foreign-keys-method=auto --recursion-method=hosts
Cannot connect to D=test,P=45009,S=/tmp/mysql_sandbox45007.sock,h=SBslave2,p=...,u=msandbox
No slaves found. See --recursion-method if host bm-support01 has slaves.
Not checking slave lag because no slaves were found and --check-slave-lag was not specified.
Operation, tries, wait:
analyze_table, 10, 1
copy_rows, 10, 0.25
create_triggers, 10, 1
drop_triggers, 10, 1
swap_tables, 10, 1
update_foreign_keys, 10, 1
No foreign keys reference `test`.`joinit`; ignoring --alter-foreign-keys-method.
Altering `test`.`joinit`...
Creating new table...
Created new table test.____joinit_new OK.
Altering new table...
Altered `test`.`____joinit_new` OK.
2018-03-12T16:39:06 Creating triggers...
2018-03-12T16:39:06 Created triggers OK.
2018-03-12T16:39:06 Copying approximately 32 rows...
2018-03-12T16:39:06 Copied rows OK.
2018-03-12T16:39:06 Analyzing new table...
2018-03-12T16:39:06 Swapping tables...
2018-03-12T16:39:06 Swapped original and new tables OK.
2018-03-12T16:39:06 Dropping old table...
2018-03-12T16:39:06 Dropped old table `test`.`_joinit_old` OK.
2018-03-12T16:39:06 Dropping triggers...
2018-03-12T16:39:06 Dropped triggers OK.
Successfully altered `test`.`joinit`.

$ pt-online-schema-change --socket=/tmp/mysql_sandbox45007.sock --user msandbox --password msandbox --execute --alter "ADD placeOfServiceCate5gor1121 BIGINT(19)" D=test,t=joinit --alter-foreign-keys-method=auto --check-slave-lag h=localhost,S=/tmp/mysql_sandbox45009.sock,u=root,p=msandbox 
Cannot connect to D=test,S=/tmp/mysql_sandbox45007.sock,h=127.0.0.1,p=...,u=msandbox
No slaves found. See --recursion-method if host bm-support01 has slaves.
Will check slave lag on:
bm-support01 -> localhost:socket
Operation, tries, wait:
analyze_table, 10, 1
copy_rows, 10, 0.25
create_triggers, 10, 1
drop_triggers, 10, 1
swap_tables, 10, 1
update_foreign_keys, 10, 1
No foreign keys reference `test`.`joinit`; ignoring --alter-foreign-keys-method.
Altering `test`.`joinit`...
Creating new table...
Created new table test.____joinit_new OK.
Altering new table...
Altered `test`.`____joinit_new` OK.
2018-03-12T16:49:59 Creating triggers...
2018-03-12T16:49:59 Created triggers OK.
2018-03-12T16:49:59 Copying approximately 32 rows...
Replica bm-support01 is stopped. Waiting.
^C# Exiting on SIGINT.
Not dropping triggers because the tool was interrupted. To drop the triggers, execute:
DROP TRIGGER IF EXISTS `test`.`pt_osc_test_joinit_del`
DROP TRIGGER IF EXISTS `test`.`pt_osc_test_joinit_upd`
DROP TRIGGER IF EXISTS `test`.`pt_osc_test_joinit_ins`
Not dropping the new table `test`.`____joinit_new` because the tool was interrupted. To drop the new table, execute:
DROP TABLE IF EXISTS `test`.`____joinit_new`;
`test`.`joinit` was not altered.