Fix vs_port provider for Red Hat platforms

https://review.openstack.org/124789 separated the interface
parameter from the port name. It added compatibility for
ovs_redhat.rb by setting resource[:interface] = @resource[:port],
however :interface was a string and is now an array, which breaks
vs_port usage.

Using @resource[:port] instead of :interface fixes the provider,
and then we need to avoid using self.bonding? and self.vlan?,
because using them causes the following error:

"Error: Could not set 'present' on ensure: private method `bonding?'
called for #<Puppet::Type::Vs_port::ProviderOvs_redhat:0x000000028e8a30>"

Change-Id: I76fba53a34ff182881022066abde0a2c5dc8d066
Closes-Bug: #1556147

lib/puppet/provider/vs_port/ovs.rb

@@ -26,14 +26,14 @@ Puppet::Type.type(:vs_port).provide(:ovs) do
     # allows this provider to be used as a base class for providers not
     # supporting all properties.
     sync_properties = []
-    if self.bonding?
+    if bonding?
       sync_properties += [:interface,
                           :bond_mode,
                           :lacp,
                           :lacp_time,
                          ]
     end
-    if self.vlan?
+    if vlan?
       sync_properties += [:vlan_mode,
                           :vlan_tag,
                           :vlan_trunks,