Docker image: (example-mongodb) the rs.initiate command in init-inventory.sh is wrong. [DBZ-1627]

Migrated from [DBZ-1627](https://issues.redhat.com/browse/DBZ-1627)

If my understanding is not wrong.
In replica set mode, the mongodb connector will lookup all node host in rs.conf().
This means: we must make sure the host that added by commnad `rs.add('host:port')` can be accessed by the connector.

However, in the init-inventory.sh, used the `hostname` as primary host （see attached hostname.jpg）.
!hostname.jpg|thumbnail!

In addition, why must we make sure all the host can be accessed by the connector ?

Start in init-inventory.sh and inspect the rs.initiate command and its configured host. Verify how the MongoDB connector resolves replica-set members, then update the command so the advertised host is accessible to the connector and confirm the example inventory setup still initializes correctly.

Written by the indexing model from the issue text.