migrateImegesToSwift: implement --dry-run flag
Migrate to both SJC and Reston
Remove unused globals
migrateImagesToSwift: log times per Swift backends
migrateImagesToSwift.php: support --dc option

And log migration time when switching Swift WF variable:

Variable wgEnableSwiftFileBackend changed value from false to true (reason: Images migration script - migration took 36 sec)
Merge pull request #2318 from Wikia/bac-1129-migrate-to-sjc-and-reston

BAC-1129 migrate images from NFS to both SJC and Reston