Creat hardlink if active apexes are in the same partition

Before the code compare the dev of the source, and target file.
However, since the target file hasn't been created at this time, the
code will always copy the source file instead of hard linkking.

Test: sideload train, and check whether the apex in rollback folder is a
hardlink. Run presubmit
Bug: 168562373

Change-Id: I6e5c6e0d35e4fa44d41d3d2d6fc564e5213e0092