NEXUS-5472: Cumulative WL fixes

Cumulative fixes gathered so far (mostly from RSO). 

Changes/Fixes:

* Repository#getLocalStatus proper handling (NEXUS-5591, NEXUS-5590)
* ProxyRepository#getProxyMode proper handling (NEXUS-5591)
* WL ThreadPool proper shutdown
* S3 scraper: did not neglect ".dot" files (NEXUS-5587)
* Apache HTTPD scraper: was too "tight" (NEXUS-5589)
* Added UTs (local status and proxy mode) and modified ITs to cover changes in NEXUS-5591

CI:
https://bamboo.zion.sonatype.com/browse/NXO-OSSF31-2
"passed" (with two unrelated failures)

CI:
https://bamboo.zion.sonatype.com/browse/NXO-OSSF31-3