test_email_change: Extract generate_email_change_link helper.
test_email_change: Extract generate_email_change_link helper.

rht/zulip,andersk/zulip,rht/zulip,zulip/zulip,andersk/zulip,rht/zulip,rht/zulip,andersk/zulip,andersk/zulip,zulip/zulip,zulip/zulip,rht/zulip,andersk/zulip,andersk/zulip,zulip/zulip,zulip/zulip,zulip/zulip,rht/zulip,zulip/zulip,rht/zulip,andersk/zulip