[FIXED JENKINS-20610] symlink FileAlreadyExistsException

Retrying 3 times while waiting for 100 millis between retries (at
recreating symlink after "deleting" it). Ends up throwing FAE exception
if thrown for a 4th time in a row - as not much can be done at that
point. A warning is logged in that case, prior to throwing the last FAE.
Merge branch 'fork_fix-fae-exception' of github.com:marco-miller/jenkins into marco-miller-fork_fix-fae-exception
[JENKINS-20610] Noting merge of #1019.