MB-9406: Check if input zip file exists or not

Change-Id: I0863852c5f1297f3431dd868e8e34fc67aaec725
Reviewed-on: http://review.couchbase.org/29855
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Bin Cui <bin.cui@gmail.com>