chore(composer): propagate errors

[ethanoroshiba]

Summary

Propagate errors which occur while composer is starting up and/or running so that the will be returned by the Composer's handle.

Background

Previously, composer would only exit with an error if the collectors' or executor's status channels were closed, and then the error message did not provide detailed information about the error that occurred. Additionally, if either of the wait_for_* loops failed, the composer would not shut down gracefully. This change is meant to expose the first eyre report which causes the composer to shut down, and gracefully shut down in all circumstances.

Changes

• Started collector and executor wait_for_ready loops concurrently, and continue with graceful shutdown even if these fail.
• Store the first error composer encounters, and return it after graceful shutdown. If waiting for collectors or executor fails, Composer continues so that it can ascertain the underlying error from the task which caused it.

Testing

Passing all tests

Changelogs

Changelog updated

Related Issues

closes #1833