[NEXUS-7581] CMA HTTP Client factory

https://issues.sonatype.org/browse/NEXUS-7581
http://bamboo.s/browse/NX-OSSF367
@mcculls Fixed by https://github.com/sonatype/nexus-oss/commit/8b56d068f252e00e2f2a4a3edde0d7f5d83c88e7