Tweak puppet config for installing PHP APC

Puppet was returning an error trying to install 'php-apc' 

```
Error: Execution of '/usr/bin/apt-get -q -y -o DPkg::Options::=--force-confold install php-apc' returned 100: Reading package lists...
Building dependency tree...
Reading state information...
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 php-apc : Depends: phpapi-20090626
E: Broken packages
```

I used php5-apc instead; APC appears to be working correctly.