NEXUS-7786: Fix for non-fatal NPE on boot

Changes:
* QZ lifecycle managed by JSR250
* Capability left but "demoted", putting scheduler in "stand-by" mode is still useful

CI
http://bamboo.s/browse/NX-OSSF427
Fixed in
https://github.com/sonatype/nexus-oss/commit/daad79cafa5258372c628d0be83c832af4435583