Nicely handle nil values for :host_ip when specifying forwarded ports

Fix GH-170

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 BUG FIXES:
 
+  - Error out in case an invalid IPs are provided for forwarded ports [#170](https://github.com/fgrehm/vagrant-lxc/issues/170)
   - Fix "Permission denied" when starting/destroying containers after lxc
     security update in Ubuntu [#180](https://github.com/fgrehm/vagrant-lxc/issues/180)
   - Fix `vagrant package` [#172](https://github.com/fgrehm/vagrant-lxc/issues/172)

lib/vagrant-lxc/action/forward_ports.rb

@@ -64,6 +64,7 @@ module Vagrant
 
           config.vm.networks.each do |type, options|
             if type == :forwarded_port && options[:id] != 'ssh'
+              options.delete(:host_ip) if options.fetch(:host_ip, '').to_s.strip.empty?
               mappings[options[:host]] = options
             end
           end

spec/unit/action/forward_ports_spec.rb

@@ -47,6 +47,15 @@ describe Vagrant::LXC::Action::ForwardPorts do
     )
   end
 
+  it 'skips --laddr parameter if host_ip is a blank string' do
+    forward_conf[:host_ip] = ' '
+    subject.stub(system: true)
+    subject.call(env)
+    subject.should have_received(:spawn).with(
+      "redir --lport=#{host_port} --caddr=#{container_ip} --cport=#{guest_port} 2>/dev/null"
+    )
+  end
+
   it "stores redir pids on machine's data dir" do
     subject.stub(system: true)
     subject.call(env)