Tests fails when mocking fs.readFileSync

[zFernand0]

The test failure has been address in the CLI repo by properly mocking fs.readFileSync but allowing yargs to use the real implementation.
See https://github.com/zowe/zowe-cli/blob/master/__mocks__/fs.ts#L52-L55

Originally posted by @zFernand0 in #53 (comment)