Fixed issue with max size for Swift objects

Fixed issue with max size of object, which Glance
should store in Swift without slicing.
Default value doesn't work when user attempts to make
a snapshots with size > 300 Mb.

Change-Id: Ic3b3120605f1e1536a34bedc4ad5c0c2f4c8510b
Closes-Bug: #1373813
Merge "Fixed issue with max size for Swift objects" into stable/5.1