CCBC-275: Do a full purge when negotiation times out

In this case we must purge the server from all commands and not simply
pop individual items. This is because we get odd behavior otherwise.

Added is a test developed with sweat and blood that reproduces the old
behavior where the client would crash.

Change-Id: Ib2c3724fde22d60388e0985a109aed8d66da9a51
Reviewed-on: http://review.couchbase.org/29671
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>