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- add SwarmAbstractionClient: a class that extends docker.Client and
  hides the API differences between the docker remote API and the
  swarm API. Thus a single docker engine can be used like a swarm

- add SharedSwarmClient: a class that extends SwarmAbstractionClient
  and monitors the swarm health and its resource (cpu/mem) and manages
  the resource allocation.
  - resources are partitioned in groups (to allow reserving resources
    for higher priority jobs)
  - two SharedSwarmClient can work together over TCP in a master/slave
    configuration (to allow the production and qualification platforms
    to use the same swarm without any interference)

- the controller is modified to:
  - use SharedSwarmClient to:
    - wait for the end of a job (in place of DockerWatcher)
    - manage resource reservation (LONG_APPS vs. BIGMEM_APPS vs normal
      apps) and monitor swarm health (fix #124)
    - NOTE: resources of the swarm and sandbox are now managed
      separately (2 instances of SharedSwarmClient), whereas it was
      global before (this was suboptimal)
  - rely on SwarmAbstractionClient to compute the cpu quotas
  - store the container_id of jobs into the DB (fix #128), this is a
    prerequisite to permit renaming apps in the future
  - store the class of the job (normal vs. long app) in the container
    name (for the resource management with SharedSwarmClient)
  - read the configuration from a yaml file (/vol/ro/config.yml) for:
    - cpu/mem quotas
    - swarm resources allocation policy
    - master/slave configuration

with swarm, we had:

2017-Apr-24 18:09:13 DEBUG    docker event b'{"from":"
node:worker1","Type":"network","Action":"disconnect","Actor":{"ID":"83192c2a09bee6e50fba8cc506b1870fb6d96438afe0a821541e00b43a7229be","Attributes":{"contain
er":"d89ab93f01cbde3e78ca2bfcc688656b15a3a664060ea85733f1497ea7531d58","name":"bridge","node.addr":"192.168.21.100:2375","node.id":"V24K:QBXP:VO3N:K2EV:M2MH:IRI4:FV7Z:LOTZ:GTTD:PDBS:SSO2:KHIG","node.ip":"192.168
.21.100","node.name":"worker1","type":"bridge"}},"time":1493050153,"timeNano":1493050153228713620,"node":{"Name":"worker1","Id":"V24K:QBXP:VO3N:K2EV:M2MH:IRI4:FV7Z:LOTZ:GTTD:PDBS:SSO2:KHIG","Addr":"192.168.21.10
0:2375","Ip":"192.168.21.100"}}'
2017-Apr-24 18:09:13 ERROR    docker watcher exception
Traceback (most recent call last):
  File "/opt/allgo-docker/controller.py", line 950, in _thread_func
      if event["status"] == "die":
      KeyError: 'status'

changing workdir /tmp -> /work is deferred to 0.6

fix #103

- sshd server installed in the toolbox
- ssh keys & config stored in ssh:/vol/cache and mounted as
  /.sandbox inside the sandbox
- toolbox mounted as /.toolbox inside the sandbox
- ssh agent & X11 forwarding are now working
- the toolbox commands available by default in every sandboxes
  (vim, less, nc, scp, ...)
- sandboxes now attached to a separate network (named
  'allgo_sandboxes' by default)

fix #88