set "HOME" after switching to netdata user

[ilyam8]

Summary

Fixes: #16511

I installed Netdata on FreeBSD using netdata-installer.sh and it failed to start service netdata start:

time=2023-12-05T15:15:26.079+02:00 comm=netdata source=daemon level=alert errno="21, Is a directory" tid=100760  msg="Cannot create required directory '/'"
0x4684bc <netdata_logger_fatal+0x1ec> at /opt/netdata/usr/sbin/netdata
0x41ece3 <set_global_environment+0x1423> at /opt/netdata/usr/sbin/netdata

The problem is:

• main.c: on this line we set the home directory to the value of the “HOME” env var.
• analytics.c: on this line we “verify” the value by creating/opening the dir and fatal on fail.

This happens before switching to the netdata user, so we are the root user. This means the value is incorrect, it is not "HOME" netdata. If you check [directory] home = in netdata.conf on your instances, you will see that it is /root. The "HOME" environment value is /root on Linux and / on FreeBSD. And the check function fails in FreeBSD => fatal.

---

The fix is:

• do not use "HOME" env variable because it points to root's home (Netdata starts as root).
• get the home directory of the user that Netdata is configured to run as and set "HOME" to it after switching to the new user.

Test Plan

Install on FreeBSD using netdata-installer.sh and make sure:

• service netdata status/stop/start/restart works.
• [directories] home in netdata.conf is set to the home directory of the user that Netdata is configured to run as (default: netdata).

Additional Information

For users: How does this change affect me?

[thiagoftsm]

On FreeBSD 13.2-RELEASE-p7 everything worked as expected, LGTM!