I'll do the review tomorrow, but for now:

$ PERCONA_TOOLKIT_BRANCH=`pwd` PERCONA_TOOLKIT_SANDBOX=~/mysql/Percona-XtraDB-Cluster-5.5.27-23.6.356.Linux.x86_64 PATH=$PERCONA_TOOLKIT_SANDBOX/bin:$PATH LD_LIBRARY_PATH=$PERCONA_TOOLKIT_SANDBOX/lib sandbox/test-env start
$ PERCONA_TOOLKIT_BRANCH=`pwd` PERCONA_TOOLKIT_SANDBOX=~/mysql/Percona-XtraDB-Cluster-5.5.27-23.6.356.Linux.x86_64 PATH=$PERCONA_TOOLKIT_SANDBOX/bin:$PATH LD_LIBRARY_PATH=$PERCONA_TOOLKIT_SANDBOX/lib prove t/pt-online-schema-change/ t/lib/
[...]
t/pt-online-schema-change/basics.t .............. 119/? # 17,20c17,19
# < # Event              Count
# < # ================== =====
# < # INSERT                 1
# < # mysql_warning_1592     1
# ---
# > # Event  Count
# > # ====== =====
# > # INSERT     1
t/pt-online-schema-change/basics.t .............. 120/? 
#   Failed test '--statistics --execute'
#   at t/pt-online-schema-change/basics.t line 688.
t/pt-online-schema-change/basics.t .............. 122/? # Looks like you failed 1 test of 122.
t/pt-online-schema-change/basics.t .............. Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/122 subtests 
	(less 1 skipped subtest: 120 okay)
[...]
t/lib/NibbleIterator.t .......................... 21/54 
#   Failed test 'SELECT chunk checksum 1 FROM sakila.country'
#   at t/lib/NibbleIterator.t line 396.
#     Structures begin differing at:
#          $got->[1] = 'd9c52498'
#     $expected->[1] = 'da79784d'
# $VAR1 = [
#   '25',
#   'd9c52498'
# ];

#   Failed test 'SELECT chunk checksum 2 FROM sakila.country'
#   at t/lib/NibbleIterator.t line 403.
#     Structures begin differing at:
#          $got->[1] = 'ebdc982c'
#     $expected->[1] = 'e860c4f9'
# $VAR1 = [
#   '25',
#   'ebdc982c'
# ];

#   Failed test 'SELECT chunk checksum 3 FROM sakila.country'
#   at t/lib/NibbleIterator.t line 410.
#     Structures begin differing at:
#          $got->[1] = 'e8d9438d'
#     $expected->[1] = 'eb651f58'
# $VAR1 = [
#   '25',
#   'e8d9438d'
# ];

#   Failed test 'SELECT chunk checksum 4 FROM sakila.country'
#   at t/lib/NibbleIterator.t line 417.
#     Structures begin differing at:
#          $got->[1] = '2e3b895d'
#     $expected->[1] = '2d87d588'
# $VAR1 = [
#   '25',
#   '2e3b895d'
# ];

#   Failed test 'SELECT chunk checksum 5 FROM sakila.country'
#   at t/lib/NibbleIterator.t line 424.
#     Structures begin differing at:
#          $got->[1] = 'bd08fd55'
#     $expected->[1] = 'beb4a180'
# $VAR1 = [
#   '9',
#   'bd08fd55'
# ];
t/lib/NibbleIterator.t .......................... 54/54 # Looks like you failed 5 tests of 54.
t/lib/NibbleIterator.t .......................... Dubious, test returned 5 (wstat 1280, 0x500)
Failed 5/54 subtests 
[...]
t/lib/SchemaIterator.t .......................... # 301c301
# < sakila.actor  CONSTRAINT `__fk_address_city` FOREIGN KEY (`city_id`) REFERENCES `city` (`city_id`) ON UPDATE CASCADE
# ---
# > sakila.actor  CONSTRAINT `fk_address_city` FOREIGN KEY (`city_id`) REFERENCES `city` (`city_id`) ON UPDATE CASCADE
# 320c320
# < sakila.category  CONSTRAINT `__fk_city_country` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`) ON UPDATE CASCADE
# ---
# > sakila.category  CONSTRAINT `fk_city_country` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`) ON UPDATE CASCADE
# 448,449c448,449
# < sakila.rental  CONSTRAINT `___fk_staff_address` FOREIGN KEY (`address_id`) REFERENCES `address` (`address_id`) ON UPDATE CASCADE
# <   CONSTRAINT `___fk_staff_store` FOREIGN KEY (`store_id`) REFERENCES `store` (`store_id`) ON UPDATE CASCADE
# ---
# > sakila.rental  CONSTRAINT `fk_staff_address` FOREIGN KEY (`address_id`) REFERENCES `address` (`address_id`) ON UPDATE CASCADE
# >   CONSTRAINT `fk_staff_store` FOREIGN KEY (`store_id`) REFERENCES `store` (`store_id`) ON UPDATE CASCADE
t/lib/SchemaIterator.t .......................... 1/? 
#   Failed test 'Iterate all schema objects with dbh'
#   at t/lib/SchemaIterator.t line 99.
t/lib/SchemaIterator.t .......................... 19/? # 34,35c34,35
# < sakila.rental  CONSTRAINT `___fk_staff_address` FOREIGN KEY (`address_id`) REFERENCES `address` (`address_id`) ON UPDATE CASCADE
# <   CONSTRAINT `___fk_staff_store` FOREIGN KEY (`store_id`) REFERENCES `store` (`store_id`) ON UPDATE CASCADE
# ---
# > sakila.rental  CONSTRAINT `fk_staff_address` FOREIGN KEY (`address_id`) REFERENCES `address` (`address_id`) ON UPDATE CASCADE
# >   CONSTRAINT `fk_staff_store` FOREIGN KEY (`store_id`) REFERENCES `store` (`store_id`) ON UPDATE CASCADE

#   Failed test 'Resume'
#   at t/lib/SchemaIterator.t line 99.
# 18,19c18,19
# < sakila.rental  CONSTRAINT `___fk_staff_address` FOREIGN KEY (`address_id`) REFERENCES `address` (`address_id`) ON UPDATE CASCADE
# <   CONSTRAINT `___fk_staff_store` FOREIGN KEY (`store_id`) REFERENCES `store` (`store_id`) ON UPDATE CASCADE
# ---
# > sakila.rental  CONSTRAINT `fk_staff_address` FOREIGN KEY (`address_id`) REFERENCES `address` (`address_id`) ON UPDATE CASCADE
# >   CONSTRAINT `fk_staff_store` FOREIGN KEY (`store_id`) REFERENCES `store` (`store_id`) ON UPDATE CASCADE

#   Failed test 'Resume from ignored table'
#   at t/lib/SchemaIterator.t line 99.
grep: /tmp/2900/data: Is a directory
t/lib/SchemaIterator.t .......................... 32/? # Looks like you failed 3 tests of 32.
t/lib/SchemaIterator.t .......................... Dubious, test returned 3 (wstat 768, 0x300)
Failed 3/32 subtests