Correct summary message for flag --findRelatedTests.

[tushardhole]

* fixes #4247
* added tests for findRelatedTests summary message

Summary
This fixes the summary message and was reported in 4247.

Test plan

1. yarn run build && yarn run test was passing

Assumptions

1. findRelatedTests can be used only when path pattern is present in args
2. if findRelatedTests is not present and path pattern is provided in args, then the summary message will always be like,
   Ran all test suites matching a.js
3. findRelatedTests & onlyChanged can not be used together
4. onlyChanged can not be used when path pattern is present in command

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[tushardhole]

@thymikee Could you please help me understand why things are failing on CI.

1. AppVeyor | locally node ./scripts/build.js is passing but same is failing here
2. test-and-deploy-website | not able to get some clue from the console
3. continuous-integration/travis-ci/pr | yarn run test-ci-partial is passing locally

[thymikee]

@tushardhole these are unrelated, so don't worry. We're just having some issues with CI servers you mentioned.

[aaronabramov]

looks good to me! thanks @tushardhole

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