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>

Makefile

@@ -18,6 +18,7 @@
 PKGNAME = snap-sync
 PREFIX ?= /usr
 SNAPPER_CONFIG ?= /etc/sysconfig/snapper
+SNAPPER_TEMPLATES ?= /etc/snapper/config-templates
 
 BIN_DIR = $(DESTDIR)$(PREFIX)/bin
 SYSTEMD_DIR = $(DESTDIR)$(PREFIX)/lib/systemd/system
@@ -27,3 +28,4 @@ SYSTEMD_DIR = $(DESTDIR)$(PREFIX)/lib/systemd/system
 install:
 	@./find_snapper_config || sed -i 's@^SNAPPER_CONFIG.*@SNAPPER_CONFIG='$(SNAPPER_CONFIG)'@g' bin/$(PKGNAME)
 	@install -Dm755 bin/* -t $(BIN_DIR)/
+	@install -Dm644 ./$(SNAPPER_TEMPLATES)/* -t $(SNAPPER_TEMPLATES)/