Add vlan configuration

This is very similar to the -cvlan capability that knife-vsphere gives you.

== DETAILS

-Added a new configuration option 'vlan' that lets you specify the vlan string
-If vlan is set, the clone spec is modified with an edit action to connect the first NIC on the VM to the configured VLAN.

== TESTING

-A new test was added to clone_spec.rb (although specs for API bindings like this mostly just test that you have wired your mocks up correctly). 

-This was tested against vSphere 5.5 both with and without selecting a new VLAN.