RFE: Add vlan tagged iscsi ports support

[Ctesias]

When a user vlan tags iscsi ports on 3par systems this driver can't find the port information required to connect initiators and fails out. I've attached a file with the ouput of the showport and showport -iscsivlan commands from the 3par system I have under test and the cinder debug logs and error:

hp3par_client_error_iscsi_port_vlans.txt

I'm willing to write the update for this feature. I wanted to have some discussion around the way the owners would prefer to see it done. I see two options:

1. Add a self.ssh.run('showport -iscsivlan') to the getPorts() method, massage the output into an array of port objects similar to what it gets from the api call, and append it to the members key of that object. Or,

2. Add a hp3par_iscsi_vlans_enabled=true flag to cinder_override.conf and create tie-ins to getPorts() to only return the output of one command or the other.

I think I'd prefer 1 since it would let people use vlans without any extra work being done by the end user. I'm open to additional options as well.