rmTargetPath can be a directory, so we have to use RemoveAll() or we
will fail to whiteout non-empty directories.
Upstream-commit: 006e2a600ce689770ba2c49805bc4f634976f365
Component: engine
When directories are white-outed we can get called with the previously
removed directories. Handle this with os.IsNotExist(error).
Upstream-commit: 6f3c32eb18f0a604ba2638b6a9f19f8824412fd1
Component: engine
Some aufs metadata are directories, and whiteouts can be for
directories, so use os.RemoveAll() for these.
Upstream-commit: 484804abffda2692492e295d4691f90564d05eb2
Component: engine
