Description of problem:

When passing the relative path to static inventory file when running a validation, the inventory is not taken in consideration. It only work if passing the absolute path. 

Version-Release number of selected component (if applicable):

- python3-validations-libs-1.0.5-1.20210326153612.4a660ec.el8ost.noarch

How reproducible:

(undercloud) [stack@undercloud-0 ~]$ openstack tripleo validator run --validation check-cpu --static-inventory inventory.yaml
Running Validations without Overcloud settings.
+--------------------------------------+-------------+--------+------------+----------------+-------------------+----------+
|                 UUID                 | Validations | Status | Host_Group | Status_by_Host | Unreachable_Hosts | Duration |
+--------------------------------------+-------------+--------+------------+----------------+-------------------+----------+
| 34a71bf3-2429-4344-9198-9258d5679baa |  check-cpu  | PASSED |    all     |                |                   |          |
+--------------------------------------+-------------+--------+------------+----------------+-------------------+----------+

(undercloud) [stack@undercloud-0 ~]$ openstack tripleo validator show run 34a71bf3-2429-4344-9198-9258d5679baa --full
{
    "plays": [
        {
            "play": {
                "duration": {
                    "start": "2021-04-26T11:21:41.016393Z"
                },
                "host": "all",
                "id": "34a71bf3-2429-4344-9198-9258d5679baa",
                "validation_id": "check-cpu",
                "validation_path": "/usr/share/ansible/validation-playbooks"
            },
            "tasks": []
        }
    ],
    "stats": {},
    "validation_output": []
}

(undercloud) [stack@undercloud-0 ~]$ openstack tripleo validator run --validation check-cpu --static-inventory /home/stack/inventory.yaml
Running Validations without Overcloud settings.
+--------------------------------------+-------------+--------+------------+-------------------------------------+-------------------+-------------+
|                 UUID                 | Validations | Status | Host_Group |            Status_by_Host           | Unreachable_Hosts |   Duration  |
+--------------------------------------+-------------+--------+------------+-------------------------------------+-------------------+-------------+
| 080355b9-7bab-4a2d-b275-690943507ee8 |  check-cpu  | FAILED |    all     | compute-0, controller-0, undercloud |                   | 0:00:02.758 |
+--------------------------------------+-------------+--------+------------+-------------------------------------+-------------------+-------------+
One or more validations have failed.


Steps to Reproduce:
1. Generate a static inventory from tripleo-ansible-inventory script
2. Run one validation with --static-inventory inventory.yaml (relative path) 
   - Validation will be considered as PASSED but real executation didn't happen, no duration etc...
3. Run one validation with --static-inventory /home/stack/inventory.yaml (absolute path)