如果gitlab runner使用docker，docker是普通配置，配置好后，runner就可以正常执行任务了。
另外一个环节Docker配置了tls加密连接，添加runner后，runner的配置tls_verify 字段值为true：
tls_verify = true
执行任务时则会报错：
ERROR: Preparation failed: error during connect: Get https://127.0.0.1:2376/v1.25/info: x509: certificate signed by unknown authority (executor_docker.go:979:0s)
搜索错误原因，提示是docker找不到tls相关的证书，但是git-runner的主机上已经配置好了证书，docker命令可以正常执行。
仔细阅读gitlab文档，在https://docs.gitlab.com/runner/configuration/advanced-configuration.html里发现了tls_cert_path这个参数，
用来配置tls证书的路径的。
在gitlab-runner的配置文件路径下/etc/gitlab-runner/config.toml，打开文件，
在runner中配置runner.docker的tls_cert_path字段值为tls文件所在路径，然后重启gitlab-runner即可
[[runners]]
name = "root_test2"
url = "http://10.10.10.10/"
token = "df6bcfdbb75332d19a7712ca23b130"
executor = "docker"
[runners.custom_build_dir]
[runners.docker]
host = "tcp://127.0.0.1:2376"
tls_verify = true
tls_cert_path = "/root/.docker/"
image = "gitlab:lasted"
privileged = false
disable_entrypoint_overwrite = false
oom_kill_disable = false
disable_cache = false
volumes = ["/root/.docker:/root/.docker","/cache"]
shm_size = 0
[runners.cache]
[runners.cache.s3]
[runners.cache.gcs]