Add require-approvals to EventFilter representation

We can request additional approval to events since c053d026
https://review.openstack.org/#/c/68516/ .  The EventFilter.__repr__ was
not displaying them though.

Change-Id: I966699e8d2daba6bd2c3bb8d57ef6d7a0e3177f2
Merge "Add require-approvals to EventFilter representation"