Delay Docker start after reboot

If external mount points are necessary for some Docker services, to make sure that Docker only starts after they have been mounted, the file /lib/systemd/system/docker.service needs to be adjusted:

[Unit]
Description=Docker Application Container Engine
Documentation=https://docs.docker.com
After=network-online.target docker.socket firewalld.service containerd.service local-fs.target remote-fs.target
Wants=network-online.target
Requires=docker.socket containerd.service
ConditionPathIsMountPoint=/mountpoint

What's changed from the default:

• local-fs.target remote-fs.target was added to After
• ConditionPathIsMountPoint was added and defines the mountpoint