Restructure testing with kbn-test package
- Run with multiple configs, move cli options to config
- Package-ify kbn-test
- Eventually we'll have functional_test_runner live in a package
of its own, and then this kbn-test will use that as a dependency,
probably still as a devDependency.
- Implement functional_tests_server
- Collapse single and multiple config apis into one command
Use kbn-es
Replace es_test_cluster + es_test_config with kbn/test utils
Implement new createEsTestCluster
Improve scripts, jsdocs, cli top-level tools
Lift error handling to the top level
