[NEXUS-5766] Walker should not give up if a collection was removed while walking it

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
Merge pull request #47 from sonatype/NEXUS-5766-snapshot-remover-ignore-inf

REVIEW: [NEXUS-5766] Walker should not give up if a collection was removed while walking it
Removed unused imports, no code change
Unused imports, no code change.
Stop Jetty HTH instance leaks.

Some AR related UTs were leaking
Jetty HTH instances, or were starting
multiple instances that were actually
not needed.
Lessen irrelevant log noise if setUp failed
No code change, unused import
Merge remote-tracking branch 'origin/master' into nexus-5749-scheduled-tasks-dissappears