node tests: Split draft_model for add/edit/delete cases.
node tests: Split draft_model for add/edit/delete cases.

This splits the one big `run_test` block into
add/edit/delete parts, for better clarity.

This also removes the `with_field` calls and
uses the override style instead, which is
preferred because it makes sure the stubbed
function is actually called.

eeshangarg/zulip,kou/zulip,kou/zulip,andersk/zulip,rht/zulip,rht/zulip,eeshangarg/zulip,andersk/zulip,zulip/zulip,kou/zulip,zulip/zulip,eeshangarg/zulip,punchagan/zulip,eeshangarg/zulip,hackerkid/zulip,kou/zulip,eeshangarg/zulip,punchagan/zulip,eeshangarg/zulip,kou/zulip,zulip/zulip,hackerkid/zulip,punchagan/zulip,kou/zulip,zulip/zulip,andersk/zulip,andersk/zulip,punchagan/zulip,rht/zulip,zulip/zulip,hackerkid/zulip,hackerkid/zulip,punchagan/zulip,punchagan/zulip,kou/zulip,eeshangarg/zulip,andersk/zulip,zulip/zulip,andersk/zulip,rht/zulip,hackerkid/zulip,hackerkid/zulip,rht/zulip,hackerkid/zulip,andersk/zulip,punchagan/zulip,rht/zulip,rht/zulip,zulip/zulip