Add documentation syncfiles examples

Also, check to make sure a syncfiles has actual
work to do before triggering a greenthread and
the client to start polling.

confluent_osdeploy/el7/profiles/default/syncfiles

@@ -0,0 +1,13 @@
+# This file lists files to synchronize or merge to the deployed systems from the deployment server
+# To specify taking /some/path/hosts on the deploymennt server and duplicating it to /etc/hosts:
+# /some/path/hosts -> /etc/hosts
+
+# If wanting to simply use the same path for source and destinaiton, the -> may be skipped:
+# /etc/hosts
+
+# Entries under MERGE will attempt to be intelligently merged. This supports /etc/group and /etc/passwd
+# Any supporting entries in /etc/shadow or /etc/gshadow are added automatically, with password disabled
+# It also will not inject 'system' ids (under 1,000 usually) as those tend to be local and rpm managed.
+MERGE:
+# /etc/passwd
+# /etc/group

confluent_osdeploy/el8/profiles/default/syncfiles

@@ -0,0 +1,13 @@
+# This file lists files to synchronize or merge to the deployed systems from the deployment server
+# To specify taking /some/path/hosts on the deploymennt server and duplicating it to /etc/hosts:
+# /some/path/hosts -> /etc/hosts
+
+# If wanting to simply use the same path for source and destinaiton, the -> may be skipped:
+# /etc/hosts
+
+# Entries under MERGE will attempt to be intelligently merged. This supports /etc/group and /etc/passwd
+# Any supporting entries in /etc/shadow or /etc/gshadow are added automatically, with password disabled
+# It also will not inject 'system' ids (under 1,000 usually) as those tend to be local and rpm managed.
+MERGE:
+# /etc/passwd
+# /etc/group

confluent_server/confluent/syncfiles.py

@@ -69,11 +69,10 @@ class SyncList(object):
             currmap[k] = v
 
 
-def sync_list_to_node(synclist, node, suffixes):
+def sync_list_to_node(sl, node, suffixes):
     targdir = tempfile.mkdtemp('.syncto{}'.format(node))
     output = ''
     try:
-        sl = SyncList(synclist)
         for ent in sl.replacemap:
             stage_ent(sl.replacemap, ent, targdir)
         if 'append' in suffixes:
@@ -144,8 +143,11 @@ def start_syncfiles(nodename, cfg, suffixes):
     synclist = '/var/lib/confluent/public/os/{}/syncfiles'.format(profile)
     if not os.path.exists(synclist):
         return '200 OK'  # not running
+    sl = SyncList(synclist)
+    if not (sl.appendmap or sl.mergemap or sl.replacemap):
+        return '200 OK'  # the synclist has no actual entries
     syncrunners[nodename] = eventlet.spawn(
-        sync_list_to_node, synclist, nodename, suffixes)
+        sync_list_to_node, sl, nodename, suffixes)
     return '202 Queued' # backgrounded
 
 def get_syncresult(nodename):