Improve checking for support for fetching IP with lxc-attach [GH-118]

lib/vagrant-lxc/action/fetch_ip_with_lxc_attach.rb

@@ -12,20 +12,14 @@ module Vagrant
 
           def call(env)
             env[:machine_ip] ||= assigned_ip(env)
-          rescue LXC::Errors::ExecuteError
-            @logger.info 'Unable to fetch IP with `lxc-attach`!'
+          rescue LXC::Errors::NamespacesNotSupported
+            @logger.info 'The `lxc-attach` command available does not support the --namespaces parameter, falling back to dnsmasq leases to fetch container ip'
           ensure
             @app.call(env)
           end
 
           def assigned_ip(env)
             driver = env[:machine].provider.driver
-            version = driver.version.match(/^(\d+\.\d+)\./)[1].to_f
-            unless version >= 0.8
-              @logger.debug "lxc version does not support the --namespaces argument to lxc-attach"
-              return nil
-            end
-
             ip = ''
             retryable(:on => LXC::Errors::ExecuteError, :tries => 10, :sleep => 3) do
               unless ip = get_container_ip_from_ip_addr(driver)

lib/vagrant-lxc/driver/cli.rb

@@ -81,7 +81,12 @@ module Vagrant
           if cmd.last.is_a?(Hash)
             opts       = cmd.pop
             namespaces = Array(opts[:namespaces]).map(&:upcase).join('|')
+
+            if run(:attach, '-h').include?('--namespaces')
               extra = ['--namespaces', namespaces] if namespaces
+            else
+              raise LXC::Errors::NamespacesNotSupported
+            end
           end
 
           run :attach, '--name', @name, *((extra || []) + cmd)

lib/vagrant-lxc/errors.rb

@@ -6,6 +6,8 @@ module Vagrant
       class ExecuteError < Vagrant::Errors::VagrantError
         error_key(:lxc_execute_error)
       end
+      class NamespacesNotSupported < Vagrant::Errors::VagrantError
+      end
 
       class LxcNotInstalled < Vagrant::Errors::VagrantError
         error_key(:lxc_not_installed)