##### 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
```

""" Populate cache using source data """
        hostvars = source_data.pop('_meta', {}).get('hostvars', {})
        for group in source_data:
            if group == 'all':
                continue
            else:
                self.inventory.add_group(group)
                hosts = source_data[group].get('hosts', [])
                for host in hosts:
                    self._populate_host_vars([host], hostvars.get(host, {}), group)
                self.inventory.add_child('all', group)
    def _populate_from_source(self, source_data, using_current_cache):
        """
        Populate inventory data from direct source
        """
        if using_current_cache:
            self._populate_from_cache(source_data)
            return source_data
        cacheable_results = {'_meta': {'hostvars': {}}}
        hostvars = {}
        objects = self.pyv._get_managed_objects_properties(vim_type=vim.VirtualMachine,
                                                           properties=['name'])
        if self.pyv.with_tags:
            tag_svc = self.pyv.rest_content.tagging.Tag
            tag_association = self.pyv.rest_content.tagging.TagAssociation
            tags_info = dict()
            tags = tag_svc.list()
            for tag in tags:
                tag_obj = tag_svc.get(tag)
                tags_info[tag_obj.id] = tag_obj.name