Implement @sshd cucumber tag hooks:

Fork an sshd server available for the duration of the scenario.

  $HOME will be set to aruba temporary directory, and a custom ssh
config will be written so that the test server is accessible with the
alias `some_host.test'. sshd will listen on port 2222 by default, this
can be overridden by setting DEFAULT_LISTEN_PORT environment variable to
the desired port.

features/support/ssh.rb

@@ -0,0 +1,106 @@
+# FIXME: should be extracted as a separate gem `cucumber-sshd?'.
+class SSHServer
+  include Aruba::Api
+
+  DEFAULT_LISTEN_PORT = 2222
+  KEY_PATH            = 'etc/ssh_host_rsa_key'
+  KEY_PUB_PATH        = KEY_PATH.dup << '.pub'
+  SSHD_CONFIG_PATH    = 'etc/sshd_config'
+  SSH_CONFIG_PATH     = '.ssh/config'
+
+  attr_accessor :listen_port
+
+  def initialize(base_path)
+    @base_path    = base_path
+    @listen_port  = ENV['PRODUCER_TEST_SSHD_PORT'] ?
+      ENV['PRODUCER_TEST_SSHD_PORT'] :
+      DEFAULT_LISTEN_PORT
+  end
+
+  def start
+    in_current_dir do
+      @pid = fork do
+        $stderr.reopen '/dev/null'
+        exec "/usr/sbin/sshd -f etc/sshd_config -Deq"
+      end
+    end
+  end
+
+  def stop
+    Process.kill('TERM', @pid)
+    Process.wait(@pid)
+  end
+
+  def make_env
+    %w[etc .ssh].map { |e| create_dir e }
+
+    write_file KEY_PATH, <<-eoh
+-----BEGIN RSA PRIVATE KEY-----
+MIIEpAIBAAKCAQEA7EVDKeM7NYCGGVJw0wWLGCoptMFSR7DobhbEx2bAQbWDLFBF
+7S9bXpW/ddebFA4GBkHVriNPwu/IGjIgO3tivVcy6iguNKdYRABlSfpeAs+OdCzK
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+iDjcFK8S1e5vnlZAh9xH1WMCEsaz1WNqWm7CZOayN2LFn6Ed9seYYg==
+-----END RSA PRIVATE KEY-----
+    eoh
+
+    write_file KEY_PUB_PATH, <<-eoh
+ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDsRUMp4zs1gIYZUnDTBYsYKim0wVJHsOhuFsTHZsBBtYMsUEXtL1telb9115sUDgYGQdWuI0/C78gaMiA7e2K9VzLqKC40p1hEAGVJ+l4Cz450LMqHIRaGYqcUxmzYyE+ImD8pR6naAVkugRyz2+STfv5wty5RWRdU5I9eVgK4eOCTBo32KP8q8Jws/i3Dzcfc/KHVaf9jiTX7edY3ZLdGBEcX1GMTHuebYWZdxmrXDKA97kbZtA29krKQv7CUogfAqIzgBalUKVzM6KWM2/0pE6EZZqchk00EgNOeKTEW9jQXKg/Wq9GsTwGWrE17Ib+9g2Zey/zGk7Qw4XrnPd3Z
+    eoh
+
+    write_file SSHD_CONFIG_PATH, <<-eoh
+Port #{listen_port}
+ListenAddress ::1
+
+Protocol 2
+HostKey #{File.expand_path @base_path}/#{KEY_PATH}
+PidFile /dev/null
+UsePrivilegeSeparation no
+ForceCommand HOME=#{File.expand_path @base_path} sh -c "cd ~; $SSH_ORIGINAL_COMMAND"
+    eoh
+
+    write_file SSH_CONFIG_PATH, <<-eoh
+Host          some_host.test
+  HostName    localhost
+  Port        #{listen_port}
+    eoh
+  end
+end
+
+
+Before('@sshd') do
+  @_sshd = SSHServer.new(current_dir)
+  @_sshd.make_env
+  @_sshd.start
+
+  ENV['HOME'] = File.expand_path current_dir
+
+  # FIXME: we might need to wait until sshd accepts connections, polling isn't
+  # really acceptable, another workaround might be to execute sshd with
+  # LD_PRELOAD and a hook, so we could block here until the hook release the
+  # blocking call.
+end
+
+After('@sshd') do
+  @_sshd.stop
+end