Have osdeploy initialize skip SSH regen

When generating new key materials, most people say 'yes' and cause problems
where they cycle valid keys without
realizing the significance.

Replace prompting with an emphasized warning instead.

confluent_server/bin/osdeploy

@@ -292,11 +292,17 @@ def initialize(cmdset):
     if cmdset.s:
         didsomething = True
         init_confluent_myname()
-        sshutil.initialize_ca()
+        try:
+            sshutil.initialize_ca()
+        except sshutil.AlreadyExists:
+            emprint('Skipping generation of SSH CA, already present and would likely be more problematic to regenerate than to reuse (if absolutely sure you want to discard old CA, then delete /etc/confluent/ssh/ca*')
     if cmdset.a:
         didsomething = True
         init_confluent_myname()
-        sshutil.initialize_root_key(True, True)
+        try:
+            sshutil.initialize_root_key(True, True)
+        except sshutil.AlreadyExists:
+            emprint('Skipping generation of new automation key, already present and regeneration usually causes more problems. (If absolutely certain, delete /etc/confluent/ssh/automation*)')
     if cmdset.p:
         install_tftp_content()
     if cmdset.l:

confluent_server/confluent/sshutil.py

@@ -72,8 +72,14 @@ def get_passphrase():
         phrase = phrase.decode('utf8')
     return phrase
 
+class AlreadyExists(Exception):
+    pass
+
 def initialize_ca():
     ouid = normalize_uid()
+    # if already there, skip, make warning
+    if os.path.exists('/etc/confluent/ssh/ca.pub'):
+        raise AlreadyExists()
     try:
         os.makedirs('/etc/confluent/ssh', mode=0o700)
     except OSError as e:
@@ -162,6 +168,8 @@ def initialize_root_key(generate, automation=False):
         for currkey in glob.glob('/root/.ssh/*.pub'):
             authorized.append(currkey)
     if automation and generate:
+        if os.path.exists('/etc/confluent/ssh/automation'):
+            raise AlreadyExists()
         subprocess.check_call(
             ['ssh-keygen', '-t', 'ed25519',
             '-f','/etc/confluent/ssh/automation', '-N', get_passphrase(),