queue: Use low-level queue_purge to empty at the end of tests.
queue: Use low-level queue_purge to empty at the end of tests.

This is O(1) at the RabbitMQ API level, and doesn't rely on the code
under test to function correctly during test cleanup.

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