CircleCI: Simplify config by using shared Orbs for testing the project and validating the podspec

[jtreanor]

This updates the CircleCI Config to use the Orbs defined in https://github.com/wordpress-mobile/circleci-orbs. It now also tests the project as well as validating the podspec.

We will be able to re-use this simple config across the other library projects in wordpress-mobile.

Related to wordpress-mobile/WordPress-iOS#10892.

It also adds cocoapods-repo-update to the Podfile to ensure that specs are always up to date.

[jkmassel]

This is fantastic!

One thing that we may want to address - in this file:

It says:

Run 'pod spec lint' on a provided .podspec file.

But we actually run pod lib lint 🙂

[jtreanor]

@jkmassel Good point! I'll change that 😄

[jklausa]

What's the difference between lib lint an spec lint?

[jkmassel]

lib lint checks to ensure that the library code in the local working directory passes tests.

spec lint downloads the most recent pod version it can find and validates that.

What that means is that if you do spec lint, you're not testing the version you're working on, you're testing the last release. Which in this case, isn't what you want :)

[jklausa]

Thanks for the explanation!