App exec with env file

When calling `kamal app exec` for new non interactive containers, run
the command per role on each server and include the role config
including the environment.

Fixes: #492

lib/kamal/cli/app.rb

@@ -147,8 +147,12 @@ def exec(cmd)
       using_version(version_or_latest) do |version|
         say "Launching command with version #{version} from new container...", :magenta
         on(KAMAL.hosts) do |host|
-          execute *KAMAL.auditor.record("Executed cmd '#{cmd}' on app version #{version}"), verbosity: :debug
-          puts_by_host host, capture_with_info(*KAMAL.app.execute_in_new_container(cmd))
+          roles = KAMAL.roles_on(host)
+
+          roles.each do |role|
+            execute *KAMAL.auditor.record("Executed cmd '#{cmd}' on app version #{version}"), verbosity: :debug
+            puts_by_host host, capture_with_info(*KAMAL.app(role: role).execute_in_new_container(cmd))
+          end
         end
       end
     end

test/cli/app_test.rb

@@ -159,7 +159,7 @@ class CliAppTest < CliTestCase
 
   test "exec" do
     run_command("exec", "ruby -v").tap do |output|
-      assert_match "docker run --rm dhh/app:latest ruby -v", output
+      assert_match "docker run --rm --env-file .kamal/env/roles/app-web.env dhh/app:latest ruby -v", output
     end
   end