Fix script to install what onos-user-key need in Docker debian:jessie image

- Install ssh package
- Create ~/.ssh directory

Change-Id: Id6e486fd63f178a6311d41b9216872ca48c61ad2
diff --git a/tools/package/bin/onos-user-key b/tools/package/bin/onos-user-key
index 8715a58..ec496f6 100755
--- a/tools/package/bin/onos-user-key
+++ b/tools/package/bin/onos-user-key
@@ -23,7 +23,8 @@
     echo "$user=$key,_g_:admingroup" >> $KEYS
 fi
 
-# ensure known_hosts file exist
+# ensure .ssh directory and known_hosts file exist
+mkdir -p $HOME/.ssh/
 (umask 077; touch "$HOME/.ssh/known_hosts")
 
 # Also, remove any previous known keys for the localhost.