instance method execute

# File lib/kamal/sshkit_with_ext.rb, line 115
    def execute
      threads = hosts.map do |host|
        Thread.new(host) do |h|
          backend(h, &block).run
        rescue ::StandardError => e
          e2 = SSHKit::Runner::ExecuteError.new e
          raise e2, "Exception while executing #{host.user ? "as #{host.user}@" : "on host "}#{host}: #{e.message}"
        end
      end

      exceptions = []
      threads.each do |t|
        begin
          t.join
        rescue SSHKit::Runner::ExecuteError => e
          exceptions << e
        end
      end
      if exceptions.one?
        raise exceptions.first
      elsif exceptions.many?
        raise exceptions.first, [ "Exceptions on #{exceptions.count} hosts:", exceptions.map(&:message) ].join("\n")
      end
    end