Added --vlan=100 to nova-manage network create

This current folsom wants to have vlan_start set or will
cause a error:

2013-02-14 23:08:32 18626 TRACE nova KeyError: 'vlan_start'

patch2 addresses comments by Alvaro Lopez, adding a link to the bug
 and removes the exception from the commit message.

Change-Id: Ic8d45c2cbbcae3b7ca635a1794e857211a4f0ccc
Merge "Added --vlan=100 to nova-manage network create"