Failing to "Migrate data" leaves target unusable

When "migrating" data failes due to insufficient space
at target location, the data copied so far is left in
target location, which in practice is now filled to the
brim.

If copy fails clean up the data copied so far since user
has the data in original location.

Bug: 26322200
Change-Id: Iab29a7f9e653e6857ee0e2723d151dfec81b14dd
1 file changed