Directly from the commit message:

• Essentially before this commit, backup request's done via REST would simply always return true. This is due to v2 endpoint to rely on exception is being thrown. If no exception occurs, it assumes that command is successful. Therefore we have aligned BackupCommand with CommandsManager by simply returning 'false' when it is successful and throwing the exception when it fails.

• Also trying to obtain stacktrace in the BackupLauncher so that user's will have the chance to track what went wrong if something goes wrong.
• Throwing a RuntimeException by default at ObservationAwareBackupExecutor because it's possible to fail the backup request when something had changed meanwhile in the version workspace. If an exception really occurs this predefined exception will be overridden anyways. If the backup execution succeeds we will be returning 'false' and hence predefined exception will not be used.