NEXUS-5790: Download speed reduced

This is a manual port of the change, that is functionally
similar, but not the same of the change in master
(wannabe 2.7.0) where whole content resource got
reimplemented.
Merge pull request #116 from sonatype/nexus-oss-2.6.x-nexus-5790

NEXUS-5790: Download speeds reduced in recent versions of Nx