Before this change, when Object.Update was called in the drive
backend, it overwrote the remote with that of the object info.
This is incorrect - the remote doesn't change on Update and this patch
fixes that and introduces a new test to make sure it is correct for
all backends.
This was noticed when doing Update of objects in a nested combine
backend.
See: https://forum.rclone.org/t/rclone-runtime-goroutine-stack-exceeds-1000000000-byte-limit/37912
65b2e378e0