Description

Steps to reproduce the issue:

1. In sonic-mgmt master branch
2. ./testbed-cli.sh start-vms server_2 password.txt

Describe the results you received:
TASK [vm_set : Retrieve a list of the defined VMs] *****************************
Monday 04 June 2018 09:24:05 +0000 (0:00:00.318) 0:00:09.696 ***********
fatal: [STR-ACS-SERV-02]: FAILED! => {"changed": false, "failed": true, "msg": "Failed to connect socket to '/var/run/libvirt/libvirt-sock': Permission denied"}

Describe the results you expected:
I want to pass this step.

Additional information you deem important:

**Output of `show version`:**

```
(paste your output here)
```

**Attach debug file `sudo generate_dump`:**

```
(paste your output here)
```