Add dumb-init to shutdown a container gracefully

[ailispaw]

https://github.com/Yelp/dumb-init

[ixkaito]

I merged your previous pull request. This seems to have conflicts with it.

[ailispaw]

I will rebase it later.

[ailispaw]

Rebased.

[ixkaito]

Many thanks!

[ailispaw]

FYI:
I found the actual problem in mysqld_safe script to stop the wocker container gracefully.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=208364#103
There is still an issue in the script (@mysql 5.5.47-0+deb8u1) as same as this report.
We need to patch mysqld_safe to add & wait at the end of the line 146 in it.

146c146
<     file) cmd="$cmd >> "`shell_quote_string "$err_log"`" 2>&1" ;;
---
>     file) cmd="$cmd >> "`shell_quote_string "$err_log"`" 2>&1 & wait" ;;

I'm not sure this was fixed in the latest mysql-server.

[ixkaito]

Thanks.
mysqld_safe now shuts down ignoring all signals, doesn't it?
Could you tell me the details of what kind of problem will occur?

[ailispaw]

Yes, I believe so.
supervisord will kill the subprocess after 10s and exit 0, because of this.
It takes a little longer to stop a container and may break files in the container.

And dumb-init can not take care of this.

[ixkaito]

Actually, I felt that stopping container takes a little longer than before.
I added a patch, and it works well.

[ailispaw]

Nice!