Add support for Centos-8

[arkodg]

No description provided.

[StefanScherer]

Build is failing

+ make VERSION=0.20200115.190524~b8797016 REVISION=b8797016bb34650f4c6dbec36e8407cc650147ec PACKAGE=containerd.io bin/containerd
+ bin/containerd
# github.com/containerd/containerd/vendor/github.com/containerd/btrfs
vendor/github.com/containerd/btrfs/btrfs.go:38:10: fatal error: btrfs/ioctl.h: No such file or directory
#include <btrfs/ioctl.h>
^~~~~~~~~~~~~~~
compilation terminated.
make: *** [Makefile:193: bin/containerd] Error 2

The Btrfs file system has been removed in Red Hat Enterprise Linux 8. This probably applies to CentOS 8, too.

[StefanScherer]

Maybe something like this https://github.com/docker/containerd-packaging/blob/master/dockerfiles/rpm.dockerfile#L31 might help, but only for centos-8, not for centos-7.

[thaJeztah]

Yes, looks like changes for RHEL8 were made in 4946024 (#83)

We should make the same changes for centos-8

[thaJeztah]

Someone should probably check if #102 is needed as well for CentOS 8

[thaJeztah]

superseded by #148