Adding eslint in system tests

[umeshp7]

All code-generators have their own eslint check but there are no eslint for lib, test, npm and index.js.
Add eslint checks to the root files and folders apart from codegen folder.

[vibhorgupta-gh]

@umeshp7 added linting, however there are a lot errors that cause a process exit. Shall I push a commit fixing them as well?

[shreys7]

@VibhorCodecianGupta this should be mentioned on the pull request and not on the issue page.😬