Test a generated Expo app too

[bryanstearns]

Generate & test an Expo app too; break up the main test into individual tests, and clean up between them.

• Wrapped all the generated tests to run them with & without Expo
• Added a utility function, expectCommandToSucceed, that enables nice simple individual tests
• Added an afterEach to clean up generated files between tests
• Added --verbose to the test command; seeing individual test progress was useful in debugging
• Removed the test for a linting script; since expo & non-expo use different commands now, didn't seem worth the complication.
• Fixed a couple of problems found by the test changes, and a race condition in storybook startup in the expo app

The bad news: after the above, test suite runtime went from 5.2m to 11.2m for me - makes sense it'd about double since we're generating a second app once, and running each of the slow generated-stuff tests twice. (I also had to increase CircleCI's timeout to get it to pass this branch.) I tried making ignite-cli a devDependency of the generated app so that I could run ignite in the tests without npx, but that didn't work right, so I reverted it.

[bryanstearns]

Closing this since it's not the right direction (but didn't want to throw away the work!)