Provide SpringApplication.exit alternative

[philwebb]

The SpringApplication.exit method seems quite hard to read. We currently document that it can be used as follows:

System.exit(SpringApplication.exit(SpringApplication.run(MyExitCodeApplication.class, args)));

It feels like a runAndExit method might be helpful:

SpringApplication.runAndExit(MyExitCodeApplication.class, args);

[wilkinsona]

What should we do about the exit code generators? Both run and exit have varargs variants:

ConfigurableApplicationContext run(Class<?> primarySource, String... args)
int exit(ApplicationContext context, ExitCodeGenerator... exitCodeGenerators)

I suspect having additional generators (beyond those that are beans) is unusual so we could have what Phil proposed above:

int runAndExit(Class<?> primarySource, String... args)

Then perhaps we should have one or more of these as well:

int runAndExit(Class<?> primarySource, ExitCodeGenerators exitCodeGenerator, String... args)
int runAndExit(Class<?> primarySource, Collection<ExitCodeGenerator> exitCodeGenerators, String... args)