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
* test case is updated.

DocImpact
Closes-Bug: #1288609
Change-Id: I8dd858e4cf17d8f689613554d1fbc3e56f220886
Merge "Fix the wrong dest of 'vlan' option and add new 'vlan_start' option"