Fix the wrong dest of 'vlan' option and add new 'vlan_start' option

Allow to specify vlan tag when create nova network, the dest of vlan
option should be 'vlan' instead of 'vlan_start'.
Provide new option 'vlan_start' when create nova network.

Change-Id: Idfaf58d4eee4d9bbf6bba5e0b6c9dbf82236694d
Closes-bug: #1329599
Merge "Fix the wrong dest of 'vlan' option and add new 'vlan_start' option"