##### SUMMARY
Environment variables in plugin do not match Tower credential injector

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
lib/ansible/plugins/inventory/vmware_vm_inventory.py

##### ANSIBLE VERSION
```
ansible 2.8.0
  config file = /etc/ansible/ansible.cfg
  configured module search path = [u'/root/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python2.7/site-packages/ansible
  executable location = /bin/ansible
  python version = 2.7.5 (default, May 20 2019, 12:21:26) [GCC 4.8.5 20150623 (Red Hat 4.8.5-36)]
```
##### CONFIGURATION
```paste below

```

##### OS / ENVIRONMENT
Red Hat Enterprise Linux Server release 7.5

##### STEPS TO REPRODUCE
use vmware inventory plugin with vCenter credential in Ansible Tower
```yaml
---
plugin: vmware_vm_inventory
validate_certs: False
```


##### EXPECTED RESULTS
inventory should be parsed

##### ACTUAL RESULTS
```paste below
 [WARNING]:  * Failed to parse
/var/lib/awx/projects/_16__ansible_inventory/tests/vmware_vm_inventory.yaml
with auto plugin: No setting was provided for required configuration
plugin_type: inventory plugin: vmware_vm_inventory setting: username
```

property_spec = vmodl.query.PropertyCollector.PropertySpec(
            type=vim_type,  
            all=False,
            pathSet=properties
        )
        
        object_spec = vmodl.query.PropertyCollector.ObjectSpec(
            obj=mor,
            skip=True,
            selectSet=[traversal_spec]
        )
        
        filter_spec = vmodl.query.PropertyCollector.FilterSpec(
            objectSet=[object_spec],
            propSet=[property_spec],
            reportMissingObjectsInResults=False
        )
        return self.content.propertyCollector.RetrieveContents([filter_spec])
    @staticmethod
    def _get_object_prop(vm, attributes):
        """Safely get a property or return None"""
        result = vm
        for attribute in attributes:
            try:
                result = getattr(result, attribute)
            except (AttributeError, IndexError):
                return None
        return result
class InventoryModule(BaseInventoryPlugin, Cacheable):