Preserve the syslog-ng.persist file on upgrades (#701)

The syslog-ng.persist file contains information about last read
systemd journal message which will prevent duplicate audit table
insertions and sending duplicate messages to remote syslog server.

truenas_install/__main__.py

@@ -450,6 +450,8 @@ def main():
                         rsync.append("var/lib/libvirt/qemu/nvram")
                     if os.path.exists(f"{old_root}/var/lib/netdata"):
                         rsync.append("var/lib/netdata")
+                    if os.path.exists(f"{old_root}/var/lib/syslog-ng/syslog-ng.persist"):
+                        rsync.append("var/lib/syslog-ng/syslog-ng.persist")
                     if "var/log" not in cloned_datasets:
                         try:
                             logs = os.listdir(f"{old_root}/var/log")

truenas_install/fhs.py

@@ -93,7 +93,8 @@ TRUENAS_DATASETS = [
     {
         'name':  'audit',
         'options': ['NOSUID', 'NOEXEC', 'NOATIME', 'NOACL'],
-        'mode': 0o700
+        'mode': 0o700,
+        'clone': True,
     },
     {
         'name':  'conf',