Allow file creation over ssh with default 755 perm

Presently files are created over ssh with the default 700 permission.
But the default permission needs to be 755 similar to that in Ubuntu.
So need to change the umask that gets set for file creation over ssh.
Add simple wrapper script for dhclient

Manila configures the second interface of the service vm by issuing
dhclient command over ssh. But cirros image has udhcpc and no dhclient.
Hence map dhclient suitably to udhcpc.