docker: added support for read-only volume access. Fix #6884

Allow specify volumes with access protection: "/var/cloud:/tmp/cloud:ro"

Mount /var/cloud with read-only access to /tmp/cloud. Try write file "echo" into write-protected directory.
```
    - name: "TEST"
      docker:
        image: ubuntu
        volumes:
          - "/var/cloud:/tmp/cloud:ro"
        command: /bin/bash -c 'echo 1 > /tmp/cloud/echo'
      tags:
        - deploy
```

Result:
```
docker ps -a
CONTAINER ID        IMAGE                  COMMAND                CREATED             STATUS              PORTS                                      NAMES
472c1e055df9        ubuntu:latest          /bin/bash -c echo 1    2 seconds ago       Exit 1

docker logs 472c1e055df9
/bin/bash: /tmp/cloud/echo: Read-only file system
```