* Initial work
* Add integration tests
* Use constants
* Fix broken code
* Handle scenario where esArgs is a string
* Remove || []
* Apply PR feedback
* Use const format
In order to make the license that applies to each file as clear as possible, and to be consistent with elasticsearch, we are adding Apache 2.0 license headers to the top of each file.
Existence of this header is enforced by eslint and tslint and missing headers were automatically added in the last commit by running:
```
node scripts/eslint --fix && node scripts/tslint --fix
```
* feat(12976): node version validation at runtime.
* refact(12976): move the code into a static utilities class.
* test(12976): added first test case using jest.
* test(12976): added test cases for node_version.
* feat(12976): create setup env node to bootstrap babel, ts-node and node version validator.
* refact(12976): migrated node version code from es6 to es5.
* feat(12976): node version validation at runtime.
* refact(12976): move the code into a static utilities class.
* test(12976): added first test case using jest.
* test(12976): added test cases for node_version.
* feat(12976): create setup env node to bootstrap babel, ts-node and node version validator.
* refact(12976): migrated node version code from es6 to es5.
* fix(12976): remove one level from ts node register cache directory link.
* chore(12976): added caret to semver dependecy in order to support minor versions.
* refact(12976): small change from named import to default import on node version validator.
* refact(12976): removed ts_node_register and add the code to babel_register.
* feat(12976): split eslint config in order to properly support files built to run before and after node version validator. refact(12976): convert script files to es5 code. refact(12976): delete inline eslint configs from node version check related files.
* refact(12976): remove ts node register file.
* refact(12976): completely port setup_node_env to es5.
* refact(12976): remove babel_register invokation from external dependencies in scripts.
* refact(12976): move node_version code directly into node_version_validator inside setup_node_env folder.
* refact(12976): only node version validator for kbn script.
