Add fallback mechanism for platforms without attach support

Some platforms (most notably CentOS and RHEL) use a kernel without
'attach' support. This patch detects this absence and falls back
to the alternative ways of doing things like detection of IP address
and halting the container.
It does so by running the command "true" through lxc-attach.

lib/vagrant-lxc/action.rb

@@ -197,8 +197,14 @@ module Vagrant
       def self.action_fetch_ip
         Builder.new.tap do |b|
           b.use Builtin::ConfigValidate
-          b.use FetchIpWithLxcAttach
+          b.use Builtin::Call, Builtin::IsState, :running do |env, b2|
-          b.use FetchIpFromDnsmasqLeases
+            if env[:result]
+              b2.use FetchIpWithLxcAttach if env[:machine].provider.driver.supports_attach?
+              b2.use FetchIpFromDnsmasqLeases
+            else
+              b2.use Builtin::Message, I18n.t("vagrant_lxc.messages.not_running")
+            end
+          end
         end
       end
 

lib/vagrant-lxc/driver.rb

@@ -113,6 +113,10 @@ module Vagrant
         @cli.destroy
       end
 
+      def supports_attach?
+        @cli.supports_attach?
+      end
+
       def attach(*command)
         @cli.attach(*command)
       end

lib/vagrant-lxc/driver/cli.rb

@@ -77,7 +77,7 @@ module Vagrant
         end
 
         def stop
-          attach '/sbin/halt'
+          attach '/sbin/halt' if supports_attach?
           run :stop, '--name', @name
         end
 
@@ -126,6 +126,19 @@ module Vagrant
           end
         end
 
+        def supports_attach?
+          unless defined?(@supports_attach)
+            begin
+              @supports_attach = true
+              run(:attach, '--name', @name, 'true')
+            rescue LXC::Errors::ExecuteError
+              @supports_attach = false
+            end
+          end
+
+          return @supports_attach
+        end
+
         private
 
         def run(command, *args)