Move FTS response validation to a separate method
Move FTS response validation to a separate method

That helps to decouple execution and validation. This change
simplifies further changes to HTTP library.

I also removed redundat exception hander. I checked all existing
FTS build logs and could not find any occurance of that exception.

Change-Id: I579d0dcb90f9fc249625395378701334973804bd
Reviewed-on: http://review.couchbase.org/76065
Reviewed-by: Alex Gyryk <0e5cab161284683621f17481c0995df0d35b63eb@couchbase.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

couchbase/perfrunner,pavel-paulau/perfrunner,couchbase/perfrunner,couchbase/perfrunner,couchbase/perfrunner,pavel-paulau/perfrunner,couchbase/perfrunner,couchbase/perfrunner,pavel-paulau/perfrunner,pavel-paulau/perfrunner,pavel-paulau/perfrunner