Support basic, dind and dind-rootless as multiple kinds of images (#619)

- `basic`: Only the runner process in the container; users need to mount the Docker socket to it.
- `dind`: A Docker daemon will be started in the container with the root user.
- `dind-rootless`: A Docker daemon will be started in the container with a rootless user.

Use s6 instead of supervisord to start processes.

Reviewed-on: https://gitea.com/gitea/act_runner/pulls/619
Reviewed-by: Zettat123 <zettat123@noreply.gitea.com>
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Jason Song <i@wolfogre.com>
Co-committed-by: Jason Song <i@wolfogre.com>

scripts/rootless.sh

@@ -1,9 +0,0 @@
-#!/usr/bin/env bash
-
-# wait for docker daemon
-while ! nc -z localhost 2376 </dev/null; do
-  echo 'waiting for docker daemon...'
-  sleep 5
-done
-
-. /opt/act/run.sh

scripts/s6/act_runner/finish

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+
+exec s6-svscanctl -t /etc/s6
+

scripts/s6/act_runner/run

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+exec run.sh

scripts/s6/docker/finish

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+
+exec s6-svscanctl -t /etc/s6
+

scripts/s6/docker/run

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+exec dockerd-entrypoint.sh

scripts/supervisord.conf

@@ -1,17 +0,0 @@
-[supervisord]
-nodaemon=true
-logfile=/dev/null
-logfile_maxbytes=0
-
-[program:dockerd]
-command=/usr/local/bin/dockerd-entrypoint.sh
-
-[program:act_runner]
-stdout_logfile=/dev/fd/1
-stdout_logfile_maxbytes=0
-redirect_stderr=true
-command=/opt/act/rootless.sh
-
-[eventlistener:processes]
-command=bash -c "echo READY && read line && kill -SIGQUIT $PPID"
-events=PROCESS_STATE_STOPPED,PROCESS_STATE_EXITED,PROCESS_STATE_FATAL