Set init stop timeout to 10 min

Summary:
bitcoind can take a long time to flush its db cache to disk upon
shutdown. Most init files send a SIGKILL after a timeout of 1 minute,
causing unclean shutdowns and triggering a long "Rolling forward" at the
next startup. Increasing this timeout to 10 minutes should reduce how
often this occurs, especially during IBD.

This is a backport of core#16569

Test Plan: NA

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9898