Update CI scripts so that command failures do not cause an immediate
exit. Prior to this commit, some of our looping logic would never run
because the entire script would exit.
Update the "sync to maven central" CI job so that it can be rerun if
necessary. We now first check if artifacts are already published before
triggering the sync from Bintray.
Closes gh-16866
Phillip Webb
Madhura Bhave
Phillip Webb