Coverty: catch exception thrown from cbsasl_pwconv
Coverty: catch exception thrown from cbsasl_pwconv

In function "main()" an exception of type "std::logic_error" is
thrown and never caught.

Change-Id: Idea9e23afda08fb064faa1310ea6057388a4070e
Reviewed-on: http://review.couchbase.org/68791
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Daniel Owen <b3fc0e1a51f252986e60be7da121b74d3ac6845f@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

daverigby/kv_engine,daverigby/memcached,couchbase/memcached,daverigby/memcached,couchbase/memcached,daverigby/kv_engine,couchbase/memcached,daverigby/kv_engine,daverigby/memcached,daverigby/kv_engine,daverigby/memcached,couchbase/memcached