##### 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
```

""" Check all requirements for this inventory are satisified"""
        if not HAS_REQUESTS:
            raise AnsibleParserError('Please install "requests" Python module as this is required'
                                     ' for VMware Guest dynamic inventory plugin.')
        elif not HAS_PYVMOMI:
            raise AnsibleParserError('Please install "PyVmomi" Python module as this is required'
                                     ' for VMware Guest dynamic inventory plugin.')
        if HAS_REQUESTS:
            
            
            required_version = (2, 3)
            requests_version = requests.__version__.split(".")[:2]
            try:
                requests_major_minor = tuple(map(int, requests_version))
            except ValueError:
                raise AnsibleParserError("Failed to parse 'requests' library version.")
            if requests_major_minor < required_version:
                raise AnsibleParserError("'requests' library version should"
                                         " be >= %s, found: %s." % (".".join([str(w) for w in required_version]),
                                                                    requests.__version__))
        if not HAS_VSPHERE and self.with_tags:
            raise AnsibleError("Unable to find 'vSphere Automation SDK' Python library which is required."
                               " Please refer this URL for installation steps"
                               " - https://code.vmware.com/web/sdk/65/vsphere-automation-python")
        if not all([self.hostname, self.username, self.password]):
            raise AnsibleError("Missing one of the following : hostname, username, password. Please read "
                               "the documentation for more information.")
    def _get_managed_objects_properties(self, vim_type, properties=None):