automation: detach policies before deleting role

You can't delete an IAM role that has attached policies.

With this change, the purge-ec2-resources command now works.

Differential Revision: https://phab.mercurial-scm.org/D6284

contrib/automation/hgautomation/aws.py

@@ -505,6 +505,10 b" def remove_resources(c, prefix='hg-'):"
 
     for role in iamresource.roles.all():
         if role.name.startswith(prefix):
+            for p in role.attached_policies.all():
+                print('detaching policy %s from %s' % (p.arn, role.name))
+                role.detach_policy(PolicyArn=p.arn)
+
             print('removing role %s' % role.name)
             role.delete()