Client: Add commandWrapper to avoid boilerplate Execute methods.
Client: Remove boilerplate genericExecute methods in favor of commandWrapper
Client: Refactor genericExecutor for easier testing.
Client: Do asynchronous commands generically instead of the WaitCommand stuff.
Client: Add file reading to genericExecuter
Client: Use genericExecutor for environment data.
Client: Add some error checking for bad types.

These should only show up during development, but errors are still nicer
than stack traces.
Client/E2E: Test that uses the client to register, deploy, and teardown an app.

Very Ooyala-specific for the moment; shouldn't be hard to factor out, though.
Client: Move a couple async calls to genericExecuter
Client: Remove some now-unused logging functions