ensure known_hosts exist

Locally running ONOS was failing on fresh machine
 where known_hosts doesn't exist yet.

Change-Id: I83beb0118f6f41e8b24eff1ab7cb53d2ca95f853
diff --git a/tools/package/bin/onos-user-key b/tools/package/bin/onos-user-key
index 9a6aff3..8715a58 100755
--- a/tools/package/bin/onos-user-key
+++ b/tools/package/bin/onos-user-key
@@ -23,6 +23,8 @@
     echo "$user=$key,_g_:admingroup" >> $KEYS
 fi
 
+# ensure known_hosts file exist
+(umask 077; touch "$HOME/.ssh/known_hosts")
+
 # Also, remove any previous known keys for the localhost.
 ssh-keygen -f "$HOME/.ssh/known_hosts" -R [localhost]:8101
-