test(addSourceModal): ds-767 lint, test updates

[cdcabrera]

What's included

• test(addSourceModal): ds-767 lint, test updates

Notes

• minor component clean up
• implementation of a getCredentialsApi get wrapper instead of a direct XHR call
• basic unit testing added

How to test

Coverage and basic unit test check

1. update the NPM packages with $ npm install
2. $ npm test
3. confirm tests come back as expected

Local run check

1. update the NPM packages with $ npm install
2. $ npm run start:stage
3. confirm adding a source still behaves as intended

Check the build

1. update the NPM packages with $ npm install
2. $ npm run build
3. confirm output comes back passing

Example

...

Updates issue/story

[nicolearagao]

lgtm