test/apiv2: fix event test to handle multiple events

Change event test assertions to check for specific image name in
Actor.Attributes instead of checking Action field. This handles
the case where DELETE operations produce multiple events.

Fixes issue where image removal produces 5-6 events instead of one.

(partial cherry-pick from commit dd1bcabae90f43dc958561322d995519f1dd2548)

Signed-off-by: Lokesh Mandvekar <lsm5@redhat.com>