History endpoint to get every history on every image

[jaguasch]

Added a new history endpoint to get information from every history on every image

GET /v1/history

Will return something like

[
  {
    "anomalies": 0,
    "image_name": "registry",
    "libs_vulns": 0,
    "os_vulns": 3,
    "reportid": "587e5346c0d56f0007f22614",
    "start_date": "2017-01-17 17:25:17.501547",
    "status": "Completed"
  },
  {
    "anomalies": 0,
    "image_name": "mongo",
    "libs_vulns": 0,
    "os_vulns": 9,
    "reportid": "587e523ac0d56f0007f22613",
    "start_date": "2017-01-17 17:21:22.946576",
    "status": "Completed"
  }
]

anomalies, libs_vulns and os_vulns are the number of results found after the anallysis of the image. reportid is the identifier of the analysis

[coveralls]

Coverage decreased (-1.2%) to 60.463% when pulling fc192a6 on jaguasch:history_all into 944d57d on eliasgranderubio:master.

[eliasgranderubio]

LGTM