Add environment-modules requirement to install Intel MPI on CentOS8

The `environment-modules` package installation automatically creates
the `/usr/share/Modules/` folder, required by the intel_mpi recipe.

## Tests
Verified installation:
```
$ rpm -qa | grep intel-mpi
intel-mpi-rt-2019.7-217-2019.7-217.x86_64
intel-mpi-doc-2019-2019.7-217.x86_64
intel-mpi-psxe-2019.7-102-2019.7-102.x86_64
intel-mpi-installer-license-2019.7-217-2019.7-217.x86_64
intel-mpi-sdk-2019.7-217-2019.7-217.x86_64
```

## References
* https://forums.centos.org/viewtopic.php?t=74035

Signed-off-by: Enrico Usai <[email protected]>

attributes/default.rb

@@ -208,7 +208,8 @@
     end
     if node['platform_version'].to_i >= 8
       # gdisk required for FSx
-      default['cfncluster']['base_packages'].push('gdisk')
+      # environment-modules required for IntelMPI
+      default['cfncluster']['base_packages'].push('gdisk', 'environment-modules')
     end
 
     default['cfncluster']['kernel_devel_pkg']['name'] = "kernel-lt-devel" if node['platform'] == 'centos' && node['platform_version'].to_i >= 6 && node['platform_version'].to_i < 7