billing: Refactor initial_upgrade to use REQ.
billing: Refactor initial_upgrade to use REQ.

kou/zulip,kou/zulip,eeshangarg/zulip,zulip/zulip,rht/zulip,eeshangarg/zulip,andersk/zulip,zulip/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,rht/zulip,kou/zulip,andersk/zulip,eeshangarg/zulip,rht/zulip,eeshangarg/zulip,kou/zulip,andersk/zulip,zulip/zulip,zulip/zulip,andersk/zulip,rht/zulip,andersk/zulip,zulip/zulip,andersk/zulip,zulip/zulip,rht/zulip,eeshangarg/zulip,andersk/zulip,rht/zulip,eeshangarg/zulip,rht/zulip,kou/zulip,kou/zulip