health-server: Adding metrics file

This commit is refactoring a little bit the code to avoid too many
parameters in functions.

Getting a dictionnary that hold all the necessary information is also
useful to dump it a "metrics" file into the benchmark directory.

This file will be used later by some analysis tool to compute some
visual results like graph or numbers.

A typical output is like :
{'affinity': {'44454c4c-4b00-1039-8050-b9c04f573032': [('10.77.7.15', 45257),
                                                       ('10.77.7.15', 44838),
                                                       ('10.77.7.15', 49190),
                                                       ('10.77.7.15', 52846),
                                                       ('10.77.7.15', 38724)],
              '44454c4c-4b00-1039-8056-b9c04f573032': [('10.77.7.15', 42045),
                                                       ('10.77.7.15', 46356),
                                                       ('10.77.7.15', 51630),
                                                       ('10.77.7.15', 35661),
                                                       ('10.77.7.15', 49982)],
              '44454c4c-4b00-1039-8058-c2c04f573032': [('10.77.7.15', 59766),
                                                       ('10.77.7.15', 40313),
                                                       ('10.77.7.15', 37087),
                                                       ('10.77.7.15', 36539),
                                                       ('10.77.7.15', 59704)]},
 'bench': {'affinity': 'fair',
           'affinity-hosts': [],
           'cores': 2,
           'hosts-list': [('10.77.7.15', 42045),
                          ('10.77.7.15', 45257),
                          ('10.77.7.15', 59766),
                          ('10.77.7.15', 46356),
                          ('10.77.7.15', 44838),
                          ('10.77.7.15', 40313),
                          ('10.77.7.15', 51630),
                          ('10.77.7.15', 49190),
                          ('10.77.7.15', 37087),
                          ('10.77.7.15', 35661),
                          ('10.77.7.15', 52846),
                          ('10.77.7.15', 36539),
                          ('10.77.7.15', 49982),
                          ('10.77.7.15', 38724),
                          ('10.77.7.15', 59704)],
           'max_hosts': 21,
           'min_hosts': 1,
           'nb_hosts': 15,
           'runtime': 10,
           'step-hosts': 3,
           'type': 2},
 'duration': {('10.77.7.15', 35661): 10.014995813369751,
              ('10.77.7.15', 36539): 10.010357856750488,
              ('10.77.7.15', 37087): 10.01489782333374,
              ('10.77.7.15', 38724): 9.975831031799316,
              ('10.77.7.15', 40313): 10.01804494857788,
              ('10.77.7.15', 42045): 10.014938831329346,
              ('10.77.7.15', 44838): 10.01133394241333,
              ('10.77.7.15', 45257): 10.014753103256226,
              ('10.77.7.15', 46356): 10.014756202697754,
              ('10.77.7.15', 49190): 10.011107921600342,
              ('10.77.7.15', 49982): 9.980446815490723,
              ('10.77.7.15', 51630): 10.010693073272705,
              ('10.77.7.15', 52846): 10.020359992980957,
              ('10.77.7.15', 59704): 9.972890138626099,
              ('10.77.7.15', 59766): 10.01703405380249},
 'hosts': [('10.77.7.15', 37087),
           ('10.77.7.15', 49982),
           ('10.77.7.15', 38724),
           ('10.77.7.15', 40313),
           ('10.77.7.15', 52846),
           ('10.77.7.15', 59704),
           ('10.77.7.15', 35661),
           ('10.77.7.15', 44838),
           ('10.77.7.15', 36539),
           ('10.77.7.15', 51630),
           ('10.77.7.15', 46356),
           ('10.77.7.15', 45257),
           ('10.77.7.15', 49190),
           ('10.77.7.15', 42045),
           ('10.77.7.15', 59766)],
 'start_lag': {('10.77.7.15', 35661): 0.05184197425842285,
               ('10.77.7.15', 36539): 0.07254815101623535,
               ('10.77.7.15', 37087): 0.07210516929626465,
               ('10.77.7.15', 38724): 0.06905198097229004,
               ('10.77.7.15', 40313): 0.06838202476501465,
               ('10.77.7.15', 42045): 0.05549502372741699,
               ('10.77.7.15', 44838): 0.06629395484924316,
               ('10.77.7.15', 45257): 0.05256390571594238,
               ('10.77.7.15', 46356): 0.05065488815307617,
               ('10.77.7.15', 49190): 0.07072901725769043,
               ('10.77.7.15', 49982): 0.05898022651672363,
               ('10.77.7.15', 51630): 0.07131385803222656,
               ('10.77.7.15', 52846): 0.06359100341796875,
               ('10.77.7.15', 59704): 0.06757187843322754,
               ('10.77.7.15', 59766): 0.06299400329589844},
 'start_time': [1409055145.752016,
                1409055145.739797,
                1409055145.750097,
                1409055145.747594,
                1409055145.743954,
                1409055145.748839,
                1409055145.73198,
                1409055145.745265,
                1409055145.753138,
                1409055145.750764,
                1409055145.729385,
                1409055145.730768,
                1409055145.750411,
                1409055145.73337,
                1409055145.741477]}