add method to set the port type()
add method to set the port type()

allows the cli to use a single method to create a port and then set the
type before calling create()

Signed-off-by: Guillermo Ontanon <d2262e90afe20c720e6771813c0217250cb2d4b2@midokura.jp>

midonet/python-midonetclient,midokura/python-midonetclient,midonet/python-midonetclient,midokura/python-midonetclient