server: use ed25519 instead of rsa when generate public/private keys (#8549)

RSA has been considered as insecure and 'ssh-rsa' signature algorithm has been deprecated in OpenSSH.

Author: weizhouapache

server/src/main/java/com/cloud/server/ConfigurationServerImpl.java

@@ -619,7 +619,7 @@ public void updateKeyPairs() {
             // FIXME: take a global database lock here for safety.
             boolean onWindows = isOnWindows();
             if(!onWindows) {
-                Script.runSimpleBashScript("if [ -f " + privkeyfile + " ]; then rm -f " + privkeyfile + "; fi; ssh-keygen -t rsa -m PEM -N '' -f " + privkeyfile + " -q 2>/dev/null || ssh-keygen -t rsa -N '' -f " + privkeyfile + " -q");
+                Script.runSimpleBashScript("if [ -f " + privkeyfile + " ]; then rm -f " + privkeyfile + "; fi; ssh-keygen -t ed25519 -m PEM -N '' -f " + privkeyfile + " -q 2>/dev/null || ssh-keygen -t ed25519 -N '' -f " + privkeyfile + " -q");
             }
 
             final String privateKey;