Provide configurable test container names for local testing

[avishnyakov]

Test containers for elastic and kibana are named "elasticsearch" and "kibana":

• go-kibana/testing_container_elasticsearch.go

  Line 27 in d7132b4

  Name: "elasticsearch",

• go-kibana/testing_container_kibana.go

  Line 35 in d7132b4

  Name: "kibana",

That naming convention might conflict with already existing containers in the system.
Might be a good idea to provide more unique name or ability to configure these names.

Stumbled naming clash while working on https://github.com/ewilde/terraform-provider-kibana repo. Running unit test locally spins these containers and might not work well if these container names already taken.

[ewilde]

@avishnyakov thank you for raising this issue, I think having unique names makes a lot of sense. Would you like to put a PR together for that?