Install containerd.io from docker on rhel_8

containerd.io is required for docker howerver it is not avilable
in official yum repos. It needs to be installed directly from
docker.

ref:
https://docs.docker.com/install/linux/docker-ce/centos/
https://linuxconfig.org/how-to-install-docker-in-rhel-8

plugins/provisioners/docker/cap/redhat/docker_install.rb

@@ -7,7 +7,12 @@ def self.docker_install(machine)
             machine.communicate.tap do |comm|
               comm.sudo("yum -q -y update")
               comm.sudo("yum -q -y remove docker-io* || true")
-              comm.sudo("curl -sSL https://get.docker.com/ | sh")
+              if machine.guest.capability("flavor") == :rhel_8
+                # containerd.io is not available on official yum repos
+                # install it directly from docker
+                comm.sudo("yum -y install https://download.docker.com/linux/centos/7/x86_64/stable/Packages/containerd.io-1.2.6-3.3.el7.x86_64.rpm")
+              end
+              comm.sudo("curl -fsSL https://get.docker.com/ | sh")
             end
 
             case machine.guest.capability("flavor")