mirroring job should rsync first and create symlink later

[Aleksandra Fedorova]

Current mirroring job takes a list of locations as input data.

Then it goes through this list and performs following steps:
1) rsync data to <timestamp> folder
2) create <latest> symlink
for every location. Which means that if rsync takes a lot of time we get <latest> symlink to point to different locations.

To minimize possible inconsistency, we should reorganize these steps in a form:

1) go through list and rsync data to <timestamp> folder

2) then go through list again and update <stable> symlinks