docker_disable_cache option is handled incorrectly

[sdclarke]

When docker_disable_cache is set to true, the --docker-disable-cache argument is passed twice, with the first instance here incorrectly having the value True passed with it.

This caused the following error when running with gitlab-runner v17.5.1 on the target machine.

FAILED! => {"changed": true, "cmd": ["/usr/bin/gitlab-runner", "register", "--non-interactive", "--url", "https://gitlab.com", "--name", "Codethink riscv-runner-4", "--executor", "docker", "--limit", "0", "--output-limit", "65536", "--docker-image", "alpine:latest", "--docker-privileged", "--docker-disable-cache", "True", "--docker-disable-cache", "--docker-volumes", "casd_socket:/run/casd", "--ssh-user", "", "--ssh-host", "", "--ssh-port", "", "--ssh-identity-file", "", "--token", "<secret>"], "delta": "0:00:00.349497", "end": "2024-10-23 17:13:13.585169", "msg": "non-zero return code", "rc": 1, "start": "2024-10-23 17:13:13.235672", "stderr": "time=\"2024-10-23T17:13:13+01:00\" level=warning msg=\"boolean parameters must be passed in the command line with --docker-disable-cache=true\"\ntime=\"2024-10-23T17:13:13+01:00\" level=warning msg=\"parameters after this may be ignored\"\nRuntime platform                                  \u001b[0;m  arch\u001b[0;m=riscv64 os\u001b[0;m=linux pid\u001b[0;m=22356 revision\u001b[0;m=affd9e7d version\u001b[0;m=17.5.1\nRunning in system-mode.                           \u001b[0;m \n                                                  \u001b[0;m \n\u001b[31;1mPANIC: The registration-token needs to be entered \u001b[0;m ", "stderr_lines": ["time=\"2024-10-23T17:13:13+01:00\" level=warning msg=\"boolean parameters must be passed in the command line with --docker-disable-cache=true\"", "time=\"2024-10-23T17:13:13+01:00\" level=warning msg=\"parameters after this may be ignored\"", "Runtime platform                                  \u001b[0;m  arch\u001b[0;m=riscv64 os\u001b[0;m=linux pid\u001b[0;m=22356 revision\u001b[0;m=affd9e7d version\u001b[0;m=17.5.1", "Running in system-mode.                           \u001b[0;m ", "                                                  \u001b[0;m ", "\u001b[31;1mPANIC: The registration-token needs to be entered \u001b[0;m "], "stdout": "", "stdout_lines": []}

Apologies for the format, the key things to note are the messages boolean parameters must be passed in the command line with --docker-disable-cache=true and parameters after this may be ignored, followed by PANIC: The registration-token needs to be entered.

For avoidance of doubt the token used in the actual run was valid but I've removed it in the paste here.

I removed my docker_disable_cache variable definition, allowing it to default to false, and confirmed that the registration worked correctly after that.