influxdb 2.x Linux package install does not restart on upgrade

[jdstrand]

Steps to reproduce:
List the minimal actions needed to reproduce the behavior.

1. install influxdb2 2.7.5 via apt-get install influxdb2=2.7.5-1
2. install influxdb2 2.7.6 via apt-get upgrade
3. observe in logs that influxdb was not restarted. Must run sudo systemctl restart influxdb

Expected behaviour:
If influxdb is running when the upgrade starts, influxdb restarts on upgrade, running any migration scripts, etc.

Actual behaviour:
influxdb is not restarted, leaving the old binary running in place. This can have security implications if the old binary had a security issue and the user upgraded thinking that was enough to effect the change. The behavior is unexpected (certainly on Debian-based systems); users understand to defer upgrades to a maintenance window but may not understand influxdb's peculiar behavior to also require a manual restart.

/var/lib/dpkg/info/influxdb.postint lacks any restart (or start, if desiring to stop in /var/lib/dpkg/info/influxdb.preinst). Please also verify rpm installs too (I did not).

Environment info:

• Using official deb packages.
• System info: Linux 4.15.0-223-generic x86_64