Intermittent failure of couchbase node API for fnFtsQuery

[Full technical run-down can be found in this forum post](https://forums.couchbase.com/t/intermittent-failure-of-couchbase-node-api-for-fnftsquery/9716).

My colleague posted the link above, will continue to update there if he finds anything else.

Summary:

In couchbase_impl.cc, in the function n1qlrow_callback, there is this code:

dataRes = jsonParseLcl->Call(Nan::GetCurrentContext()->Global(), 1, &metaStr);

This code fails in an unrecoverable way (at the nodeJS layer) when it receives garbled or bad JSON responses from the couchbase server. The way this manifests in nodeJS is as an error without a stack trace, which can't be caught and terminates the program.

Root cause appears to be garbled "metrics" JSON data coming back from the server, causing an attempt to parse resulting JSON to fail, but unable to tell the source of the bad JSON, whether in the C library or coming from the server.