Catch any sort of network error in connection tests

libcouchbase tends to change the specific type of network error being
thrown in certain conditions.
We should catch these as part of CouchbaseNetworkError than fish
between versions.

Change-Id: I8153a3c9bb46745e8cee260e82095192c0cbbfe2
Reviewed-on: http://review.couchbase.org/30802
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>