Make clear-docker-cache script to work for Docker versions below 17.06.1

What does this MR do?

This MR makes the clear-docker-cache script to work for Docker versions below 17.06.1

Why was this MR needed?

Currently, the clear-docker-cache script fails when using a Docker version between 1.13 and 17.06.1.

[root@gitlab-runner ~]# gitlab-runner --version
Version:      14.9.1
Git revision: f188edd7
Git branch:   14-9-stable
GO version:   go1.17.7
Built:        2022-03-22T20:45:44+0000
OS/Arch:      linux/amd64

[root@gitlab-runner ~]# docker version
Client:
 Version:         1.13.1
 API version:     1.26
 Package version: docker-1.13.1-209.git7d71120.el7_9.x86_64
 Go version:      go1.10.3
 Git commit:      7d71120/1.13.1
 Built:           Fri Jan  7 13:15:46 2022
 OS/Arch:         linux/amd64

Server:
 Version:         1.13.1
 API version:     1.26 (minimum version 1.12)
 Package version: docker-1.13.1-209.git7d71120.el7_9.x86_64
 Go version:      go1.10.3
 Git commit:      7d71120/1.13.1
 Built:           Fri Jan  7 13:15:46 2022
 OS/Arch:         linux/amd64
 Experimental:    false

[root@gitlab-runner ~]# /usr/share/gitlab-runner/clear-docker-cache

Check and remove all unused containers (both dangling and unreferenced) including volumes.
------------------------------------------------------------------------------------------


unknown flag: --volumes
See 'docker system prune --help'.

The --volumes flag in docker system prune was introduced in Docker client version 17.06.1: https://docs.docker.com/engine/release-notes/17.06/#client-1

What's the best way to test this MR?

Test script with different Docker versions (1.13, 17.06.1)

What are the relevant issue numbers?

No issue opened