Make it possible to disable overlay and overlay2 separately.
With this commit, we now have `exclude_graphdriver_overlay` and
`exclude_graphdriver_overlay2` build tags for the engine, which
is in line with any other graph driver.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Adds a new overlay driver which uses multiple lower directories to create the union fs.
Additionally it uses symlinks and relative mount paths to allow a depth of 128 and stay within the mount page size limit.
Diffs and done directly over a single directory allowing diffs to be done efficiently and without the need fo the naive diff driver.
Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)
Daniel Nephin