Can you try updating percona-release to version 0.1-3 and then run yum update or yum install percona-toolkit again.
I've updated from percona-release-0.0-1.x86_64 to percona-release-0.1-3.noarch and then upgrade worked. Somehow with the older percona-release version the new percona-toolkit was not detected.

[root@node1 ~]# yum -q list percona-toolkit
Installed Packages
percona-toolkit.noarch                                                                  2.2.11-1                                                                  @percona
[root@node1 ~]# uname -a
Linux node1 3.13.0-36-generic #63-Ubuntu SMP Wed Sep 3 21:30:07 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

[root@node1 ~]# yum install percona-toolkit
Loaded plugins: fastestmirror
Setting up Install Process
Loading mirror speeds from cached hostfile
 * base: mirror.23media.de
 * epel: mirrors.n-ix.net
 * extras: mirror.softaculous.com
 * updates: mirror.softaculous.com
Package percona-toolkit-2.2.11-1.noarch already installed and latest version
Nothing to do

[root@node1 ~]# yum install percona-release
-- cut --
Running Transaction
  Updating   : percona-release-0.1-3.noarch                                                                                                                           1/2 
  Cleanup    : percona-release-0.0-1.x86_64                                                                                                                           2/2 
  Verifying  : percona-release-0.1-3.noarch                                                                                                                           1/2 
  Verifying  : percona-release-0.0-1.x86_64                                                                                                                           2/2 

Updated:
  percona-release.noarch 0:0.1-3                                                                                                                                          

Complete!

[root@node1 ~]# yum install percona-toolkit
-- cut --
Running Transaction
  Updating   : percona-toolkit-2.2.12-1.noarch                                                                                                                        1/2 
  Cleanup    : percona-toolkit-2.2.11-1.noarch                                                                                                                        2/2 
  Verifying  : percona-toolkit-2.2.12-1.noarch                                                                                                                        1/2 
  Verifying  : percona-toolkit-2.2.11-1.noarch                                                                                                                        2/2 

Updated:
  percona-toolkit.noarch 0:2.2.12-1                                                                                                                                       

Complete!
[root@node1 ~]# yum -q list percona-toolkit
Installed Packages
percona-toolkit.noarch                                                          2.2.12-1                                                           @percona-release-noarch
[root@node1 ~]# pt-online-schema-change --version
pt-online-schema-change 2.2.12