Merge pull request #40368 from sc68cal/patch/centos_name

Automatic merge from submit-queue (batch tested with PRs 40111, 40368, 40342, 40274, 39443)

Change OPENSTACK_IMAGE_NAME to be more specific

There may already be other images in the cloud named CentOS7,
but since we are fetching a very specific version (1604) we should
go ahead and make the image name very specific as well.



**What this PR does / why we need it**:

Some clouds already have `Centos7` as an image that is available, however it may not be the *specific* version that openstack-heat looks for and downloads from CentOS.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: 

**Special notes for your reviewer**:

**Release note**:

```release-note 
OpenStack-Heat will now look for an image named "CentOS-7-x86_64-GenericCloud-1604". To restore the previous behavior set OPENSTACK_IMAGE_NAME="CentOS7"
```

cluster/openstack-heat/config-image.sh

@@ -17,7 +17,7 @@
 ## Contains configuration values for new image. It is skip when CREATE_IMAGE=false
 
 # Image name which will be displayed in OpenStack
-OPENSTACK_IMAGE_NAME=${OPENSTACK_IMAGE_NAME:-CentOS7}
+OPENSTACK_IMAGE_NAME=${OPENSTACK_IMAGE_NAME:-CentOS-7-x86_64-GenericCloud-1604}
 
 # Downloaded image name for Openstack project
 IMAGE_FILE=${IMAGE_FILE:-CentOS-7-x86_64-GenericCloud-1604.qcow2}