engine : creating storage connection with empty port, port is set to 0

When creating a storage connection if an empty
port is passed the value is set to 0.

A new validation has been added to canDoAction
that verifies that the port is greater than zero.

Change-Id: Ief68a9b65946d88e3eace6f21fc887ea373725b1
Bug-Url: https://bugzilla.redhat.com/1006449
Signed-off-by: Ravi Nori <rnori@redhat.com>