use anchor pattern to fix containment of uchiwa class

Basically, I could not create a correct order structure from the outside, like:
```puppet
class { 'sensu':
  manage_repo => true
}

class { 'uchiwa':
  manage_repo => false,
  require => Class['sensu']
}
```
would still lead to having the uchiwa::install class being executed before the sensu class could add the right repository. With the anchors I added it should be fixed.