Verify and fix BDB multi node deployment guide

- Documentation support to add a new BDB node to an existing
  replica set, using x.509 certificates and SSL/TSL connections, across
  geographically dispersed clusters.
- Fix some documentation issues and add more references i.e.
  specifically about signing of MongoDB member certificates.
- Minor fixes for nginx-https-dep.yaml(invalid configMap var)
- Reconfigure nginx keep_alive between MongoDB front and backend ports.
- Editor removed whitespaces

k8s/nginx-https/nginx-https-dep.yaml

@@ -59,7 +59,7 @@ spec:
           valueFrom:
             configMapKeyRef:
               name: vars
-              key: openresty-instance-name
+              key: ngx-openresty-instance-name
         - name: BIGCHAINDB_BACKEND_HOST
           valueFrom:
             configMapKeyRef: