improve port option validation

[lei zhang]

Option port only has a default value, so i think it will have some errors
when setting port outside the range of 1-65535

eg:
    cfg.IntOpt('port',
            default=9511,
            help='The port for the Magnum API server.')

According to http://docs.openstack.org/developer/oslo.config/cfg.html，
oslo.config can use portType to support the ability to set valid range
on port option values

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/217064

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/217064
Committed: https://git.openstack.org/cgit/openstack/magnum/commit/?id=d14382d997e7aa9c7d1dc891112ba252a1208a83
Submitter: Jenkins
Branch: master

commit d14382d997e7aa9c7d1dc891112ba252a1208a83
Author: lei-zhang-99cloud <[e-mail]>
Date: Wed Aug 26 17:48:17 2015 +0800

    Add port type on port option

    According to http://docs.openstack.org/developer/oslo.config/cfg.html
    oslo.config can use portType to support the ability to set valid range
    on port option values

    Closes-Bug: #1488861

    Change-Id: Ic4310532f4155ade1706f0bca8df9466665aea97