NEXUS-7761: Forward-port of "DirSupport.move simplification"

Commits (from 2.11.x):
e9c3d195ccb298c445549367c22fe076705d548c
63c3216b1a92e24d7e11b83f58f9cef20d43eb16
3a1021fed73b1be021f4e3ebe21e124ee54b49d9
7a1dee7b1304a65a1d247367a4f1932c786999cd
13ec6b7dd2c44beabc5370652b4e26f1cd3c378a
f3732eb2105e2a21554d69311d12a5df8395e275
7afbca747265bc8a42c1559e22ea701c2b5802dd

These above contain PR but has more than the PR
https://github.com/sonatype/nexus-oss/pull/772

CI
http://bamboo.s/browse/NX-OSSF426