Pin the percona repo 

When I tried installing on a ubuntu - precise x86_64 , it bombed with 
```
[2013-01-23T16:18:55-02:00] INFO: Processing package[libmysqlclient-dev] action install (percona::package_repo line 21)
[2013-01-23T16:20:19-02:00] INFO: Processing package[percona-server-server] action install (percona::server line 6)

================================================================================
Error executing action `install` on resource 'package[percona-server-server]'
================================================================================
```

Later i found the issue being libmysqlclient-dev package coming from another repo and that created a whole bunch of conflicts.

Pinning the percona repo with high priority solved it - (libmysqlclient-dev got installed from the percona repo)