feat: Fixed a bug when assigning stemcell_ids

- Stemcell ids is an array and not a string

Co-authored-by: Joe Eltgroth <joe.eltgroth@broadcom.com>
Co-authored-by: Ramkumar Vengadakrishnan <ramkumar.vengadakrishnan@broadcom.com>

tile_generator/opsmgr.py

@@ -408,7 +408,7 @@ def configure(product, properties, strict=False, skip_validation=False, network=
 		else:
 			raise Exception("Cannot find cf stemcell to use")
 		print('- Using stemcell id', stemcell)
-		product_settings['stemcell_ids'] = stemcell
+		product_settings['stemcell_ids'][0] = stemcell
 		post_yaml('/api/installation_settings', 'installation[file]', settings)
 	#
 	# Use the first availability zone (skip this for Azure, which doesn't use them)