Data race that has been seen:
```
Read at 0x00c00134bec0 by goroutine 159:
github.com/nats-io/nats-server/v2/server.(*client).msgHeaderForRouteOrLeaf()
/home/travis/gopath/src/github.com/nats-io/nats-server/server/client.go:2935 +0x254
github.com/nats-io/nats-server/v2/server.(*client).processMsgResults()
/home/travis/gopath/src/github.com/nats-io/nats-server/server/client.go:4364 +0x2147
(...)
Previous write at 0x00c00134bec0 by goroutine 201:
github.com/nats-io/nats-server/v2/server.(*Server).addRoute()
/home/travis/gopath/src/github.com/nats-io/nats-server/server/route.go:1475 +0xdb4
github.com/nats-io/nats-server/v2/server.(*client).processRouteInfo()
/home/travis/gopath/src/github.com/nats-io/nats-server/server/route.go:641 +0x1704
```
Also fixed some flappers and removed use of `s.js.` since we have
already captured `js` in Jsz monitoring.
Signed-off-by: Ivan Kozlovic <ivan@synadia.com>