On some environment such as CentOS8, journalctl --user -xe does not work
since journald is running in volatile mode.
The issue cannnot fix in non-root mode, as a workaround we should logging to
a file instead of journal.
Also added scylla_logrotate to ExecStartPre which rename previous log file,
since StandardOutput=file:/path/to/file will erase existing file when service
restarted.
Fixes#7131Closes#7326
0f786f05fe