MB-12048: Add test for upgrading header from 2.x to 3.x

There was a unit test missing that the upgrading from a Couchbase 2.x
to a 3.x view file really works.

Change-Id: I819f7a1594e73765223871da5f1652826f1b926c
Reviewed-on: http://review.couchbase.org/42933
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Nimish Gupta <nimish@couchbase.com>
Tested-by: Volker Mische <volker.mische@gmail.com>