Rework resources import

[treywelsh]

Description

Some resources have specific import method like address range. It appears that sometimes I'm fixing the reading method of the resource instead of introducing an import method to set some empty attributes..

New or affected resources and data sources

• opennebula_virtual_machine

And I probably forgot some other I'll need to check each resources

This shouldn't impact the resources behavior other than improving the import and maybe the reading behaviors

References

For instance for the virtual machine:
#312
#356