snap-sync: enable snapper to admin snap-sync backups on target

- create and verify snapper compatible structure on target host
- create snapper config (snap-$selected_config) on target host
  if not already available. use a snap-sync template.
- change userdata for snapper listings on target config
  subvolid, uuid and hostname reflact the values from the source system
- introduce a snapper template (/etc/snapper/config-templates/snap-sync)
- adapt Makefile to support an initial snap-sync template
  per default, this templates excludes snap-sync backup configs
  from timeline and cleanup tasks

Signed-off-by: Ralf Zerres <ralf.zerres@networkx.de>

etc/snapper/config-templates/snap-sync

@@ -0,0 +1,58 @@
+###
+# snapper template for snap-sync handling
+###
+
+# subvolume to snapshot
+SUBVOLUME="/var/lib/snap-sync"
+
+# filesystem type
+FSTYPE="btrfs"
+
+
+# users and groups allowed to work with config
+ALLOW_USERS=""
+ALLOW_GROUPS="adm"
+
+# sync users and groups from ALLOW_USERS and ALLOW_GROUPS to .snapshots
+# directory
+SYNC_ACL="yes"
+
+
+# start comparing pre- and post-snapshot in background after creating
+# post-snapshot
+BACKGROUND_COMPARISON="yes"
+
+
+# run daily number cleanup
+NUMBER_CLEANUP="no"
+
+# limit for number cleanup
+NUMBER_MIN_AGE="1800"
+NUMBER_LIMIT="50"
+NUMBER_LIMIT_IMPORTANT="10"
+
+# "no": we will use systemd.timer
+TIMELINE_CREATE="no"
+
+# create cron based cleanup entries
+# "no": we will use systemd.timer
+TIMELINE_CLEANUP="no"
+
+# snap-sync: timeline settings
+TIMELINE_MIN_AGE="1800"
+TIMELINE_LIMIT_HOURLY="1"
+TIMELINE_LIMIT_DAILY="2"
+TIMELINE_LIMIT_MONTHLY="1"
+TIMELINE_LIMIT_YEARLY="1"
+
+
+# cleanup empty pre-post-pairs
+EMPTY_PRE_POST_CLEANUP="yes"
+
+# limits for empty pre-post-pair cleanup
+EMPTY_PRE_POST_MIN_AGE="1800"
+
+# uncomment to exclude this subvol when calling
+# snap-sync as timer unit
+# SNAP_SUNC_EXCLUDE="yes" 
+