slaprunner/sshd: Add support for sftp

For sftp to work we need to define sftp "subsystem" on server side in
sshd speak. Sftp support in turn allows for sshfs to work.

NOTE

	Subsystem sftp internal-sftp

won't work because we are doing games with ForceCommand and reexecution
of "$SSH_ORIGINAL_COMMAND" (see previous patch for details).

software/slaprunner/common.cfg

@@ -60,7 +60,7 @@ mode = 0644
 recipe = slapos.recipe.template
 url = ${:_profile_base_location_}/instance-runner.cfg
 output = ${buildout:directory}/template-runner.cfg.in
-md5sum = 8f7f649d1de6149f028d1442e7dfa593
+md5sum = 0b3561ee4ef8d687fa95f2915fe9923b
 mode = 0644
 
 [template-runner-import-script]

software/slaprunner/instance-runner.cfg

@@ -223,6 +223,7 @@ template = inline:
   PubkeyAuthentication yes
   AuthorizedKeysFile $${buildout:directory}/.ssh/authorized_keys
   ForceCommand if [ -z "$SSH_ORIGINAL_COMMAND" ]; then ${bash:location}/bin/bash -l; else eval "$SSH_ORIGINAL_COMMAND"; fi
+  Subsystem sftp ${openssh:location}/libexec/sftp-server
 
 [runner-sshd-raw-server]
 recipe = slapos.cookbook:wrapper