entity_delete edge case: problems when entity belongs to a container set

[noblem]

From Chip Stewart:

Hi Mike, 

 fissfc entity_delete  has a somewhat obscure error message when attempting to delete an entity that belongs to a set. 

$ fissfc -y entity_delete -w rebc_template -p rebc-oct16 -t pair -e ACBL-NT-NB
Error 409: [{u'entityName': u'ACBL-NT-NB', u'entityType': u'pair'}, {u'entityName': u'REBC-NT-NB-99', u'entityType': u'pair_set'}, {u'entityName': u'REBC-PILOT-NT-NB-24', u'entityType': u'pair_set'}]

After deleting the pair sets REBC-NT-NB-99 and REBC-PILOT-NT-NB-24, I was able to delete pair ACBL-NT-NB, which makes some sense,  but it took me a day or so of playing around with fiss, firecloud api & python version before I realized that the pair_sets were blocking the delete. 

Is there someone in your group who could add the tip about sets to the message for error 409 ?

[sammeier]

If the preference is merely for a notification, I've made a branch entity_delete_409_patch with some proposed language. If the goal is for a larger suggested resolution, this may require some discussion.