[WFLY-543] : Provide an operation to request service status report after server has been started

Adding the new command "read-boot-errors" available from core-service=management to list all operations that failed during boot.
It displays all boot errors with the failed operation and the failure description / exception of the error.
Jira: https://issues.jboss.org/browse/WFLY-543
This should be the first line in the finally block at the end of executeStep.

It probably doesn't matter that it's here, because we no longer support the original recursive completeStep() variant that would have caused this code to get executed at the wrong time if it was left here. But, I'm extremely fussy about this logic. :) Partly because if I ever rip out the old support for the recursive behavior, I want to start from a point where everything is where it should have been.