Skip existing containers on accessory boot

When booting an accessory, check for the container first and skip boot
if it exists. This allows us to rerun `kamal setup` on hosts with
accessories without raising an error.

Fixes: https://github.com/basecamp/kamal/issues/488

lib/kamal/cli/accessory.rb

@@ -1,4 +1,5 @@
 require "active_support/core_ext/array/conversions"
+require "concurrent/array"
 
 class Kamal::Cli::Accessory < Kamal::Cli::Base
   desc "boot [NAME]", "Boot new accessory service on host (use NAME=all to boot all accessories)"
@@ -10,6 +11,16 @@ class Kamal::Cli::Accessory < Kamal::Cli::Base
         prepare(name) if prepare
 
         with_accessory(name) do |accessory, hosts|
+          booted_hosts = Concurrent::Array.new
+          on(hosts) do |host|
+            booted_hosts << host.to_s if capture_with_info(*accessory.info(all: true, quiet: true)).strip.presence
+          end
+
+          if booted_hosts.any?
+            say "Skipping booting `#{name}` on #{booted_hosts.sort.join(", ")}, a container already exists", :yellow
+            hosts -= booted_hosts
+          end
+
           directories(name)
           upload(name)
 

lib/kamal/commands/accessory.rb

@@ -37,8 +37,8 @@ class Kamal::Commands::Accessory < Kamal::Commands::Base
     docker :container, :stop, service_name
   end
 
-  def info
-    docker :ps, *service_filter
+  def info(all: false, quiet: false)
+    docker :ps, *("-a" if all), *("-q" if quiet), *service_filter
   end
 
   def logs(timestamps: true, since: nil, lines: nil, grep: nil, grep_options: nil)