Rename hostRequires to host_requires
Naming convention for kpet and kpet-db's YAML is snake_case. hostRequires
wasn't following this convention, so it's been changed here.
This change need the update of kpet-db/index.yaml in order to work.
Maybe it would be a good idea to create a new test or test case for assuring that this attribute doesn't break anything. Not sure if it's necessary for this case.