do the simple puppet-lint errors

Hi Nick,

I ran the manifests through puppet-lint, which follows the [style guide](https://docs.puppetlabs.com/guides/style_guide.html). I didn't use the 80character line check, as I dont use this one check myself.

FYI, here are the remaining errors that will require more effort. Many of these are due to the use of inheritance, which is no longer recommended. 
```
icinga2/manifests ❯ puppet-lint --no-80chars-check --with-filename .
./nrpe.pp - WARNING: class inheriting from params class on line 16
./nrpe/install.pp - ERROR: icinga2::nrpe::install::repos not in autoload module layout on line 20
./nrpe/install.pp - ERROR: icinga2::nrpe::install::packages not in autoload module layout on line 30
./nrpe/install.pp - ERROR: icinga2::nrpe::install::execs not in autoload module layout on line 45
./nrpe/config.pp - WARNING: top-scope variable being used without an explicit namespace on line 13
./server.pp - WARNING: class inheriting from params class on line 25
./server/install.pp - ERROR: icinga2::server::install::repos not in autoload module layout on line 29
./server/install.pp - ERROR: icinga2::server::install::packages not in autoload module layout on line 68
./server/install.pp - ERROR: icinga2::server::install::execs not in autoload module layout on line 105
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 75
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 78
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 82
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 87
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 99
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 110
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 116
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 116
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 116
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 116
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 135
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 135
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 135
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 135
./server/install.pp - WARNING: top-scope variable being used without an explicit namespace on line 149
./server/install.pp - WARNING: class not documented on line 29
```

This pull request should supsersede #1