Fixed AttributeError when attempting to destroy AWS instances

The provider argument provided is of type Providers enum which has no upper function.

The error produced was

AttributeError: 'Providers' object has no attribute 'upper'

Ticket: ENT-13656
Changelog: title

Co-authored-by: Ole Herman Schumacher Elgesem <4048546+olehermanse@users.noreply.github.com>

Author: craigcomstock

cf_remote/commands.py

@@ -546,7 +546,9 @@ def _delete_saved_group(vms_info, group_name):
 
 def _get_cloud_vms(provider, creds, region, group):
     if creds is None:
-        raise CFRExitError("Missing/incomplete {} credentials".format(provider.upper()))
+        raise CFRExitError(
+            "Missing/incomplete {} credentials".format(str(provider).upper())
+        )
     driver = get_cloud_driver(provider, creds, region)
 
     assert driver is not None