There are two cases where we can't use a graphdriver:
1) the graphdriver itself isn't supported by the system
2) the graphdriver is supported by some configuration/prerequisites are
missing
This introduces a new error for the 2) case and uses it when trying to
run docker with btrfs backend on a non-btrfs filesystem.
Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Upstream-commit: 75754e69f6cce80c34ebc72817ada0a807fd635a
Component: engine
32c2485efa