fix: make converter compatible with older PyYAML

[btravouillon]

CentOS 8 ship with PyYAML 3.12 while I used some features introduced
with 5.1, which are incompatible. See yaml/pyyaml#265.

It appears I tested it in my virtualenv setup with latest PyYAML 5.3.1.... 👎

[btravouillon]

Without this patch, the code fails on CentOS 8 while converting the inventory files:

[root@management1 bluebanquise]# ./tools/inventory-converter-1.3-network_interfaces.py inventory/cluster/nodes/computes.yml 
Traceback (most recent call last):
  File "./tools/inventory-converter-1.3-network_interfaces.py", line 77, in <module>
    main()
  File "./tools/inventory-converter-1.3-network_interfaces.py", line 63, in main
    inventory = yaml.load(fd, Loader=yaml.FullLoader)
AttributeError: module 'yaml' has no attribute 'FullLoader'

[oxedions]

Hello,

I had same kind of issues on Centos.

Merging.