SshDaemon: Add implementation of InsecureBouncyCastleRandom.random()

Copied from org.apache.sshd.common.random.BouncyCastleRandom

Change-Id: Ie12d7fd85eeeb38c380e73f2006026572128b7a9

gerrit-sshd/src/main/java/com/google/gerrit/sshd/SshDaemon.java

@@ -439,8 +439,29 @@ public class SshDaemon extends SshServer implements SshInfo, LifecycleListener {
 
     @Override
     public int random(int n) {
-      // TODO Auto-generated method stub
-      return 0;
+      if (n > 0) {
+        if ((n & -n) == n) {
+          return (int)((n * (long) next(31)) >> 31);
+        }
+        int bits, val;
+        do {
+          bits = next(31);
+          val = bits % n;
+        } while (bits - val + (n-1) < 0);
+        return val;
+      }
+      throw new IllegalArgumentException();
+    }
+
+    final protected int next(int numBits) {
+      int bytes = (numBits+7)/8;
+      byte next[] = new byte[bytes];
+      int ret = 0;
+      random.nextBytes(next);
+      for (int i = 0; i < bytes; i++) {
+        ret = (next[i] & 0xFF) | (ret << 8);
+      }
+      return ret >>> (bytes*8 - numBits);
     }
   }