NEXUS-6537: Do a move when possible

Perform real move when possible. Same limitation stands on Java7 Files class as before (move on non-empty directory is possible only if on same partition, subtree does not have to be moved), but this time there are means to detect does this stand or not.

Issue
https://issues.sonatype.org/browse/NEXUS-6537

CI
http://bamboo.s/browse/NX-OSSF78
Unsure about this. We should try the atomic-move, then non-atomic-move (which is still superb related to copy+delete), and then fallback to copy+delete?