health-start: Adding host in start-time (metrics)

When dumping the start-time in the metrics output, it's mandatory to
report the associated host to allow some later computation on it.
health-server: Renaming nb_hosts to nb-hosts

To avoid confusions when writing code, let's get all the variable under
the same format "-" and not "_"
health: Dump message only print in debug mode

There is no need to print the dump message everytime a host completed.
That's very boring to read and makes the output confusing to read.
health: Printing number of loops and not number of hosts

When running the benchmark, it's much more easy to get the number of
expected loops instead of the number of hosts.

As a result the output looks like :

INFO:health_protocol:Starting logger
INFO:health_protocol:Starting server
INFO:health_protocol:Results will be stored in /var/lib/edeploy/health/dahc/cpu_load/2014_08_26-12h44
INFO:health_protocol:Expecting 21 hosts to start job cpu_load
INFO:health_protocol:Still 20 hosts to connect
INFO:health_protocol:Still 17 hosts to connect
INFO:health_protocol:Still 15 hosts to connect
INFO:health_protocol:Still 10 hosts to connect
INFO:health_protocol:Still 8 hosts to connect
INFO:health_protocol:Still 6 hosts to connect
INFO:health_protocol:Still 5 hosts to connect
INFO:health_protocol:Still 1 hosts to connect
INFO:health_protocol:Starting job cpu_load
INFO:health_protocol:CPU: Waiting bench 1 / 8 to finish on 1 hosts (step = 3): should take 10 seconds
INFO:health_protocol:CPU: Waiting bench 2 / 8 to finish on 3 hosts (step = 3): should take 10 seconds
INFO:health_protocol:CPU: Waiting bench 3 / 8 to finish on 6 hosts (step = 3): should take 10 seconds
INFO:health_protocol:CPU: Waiting bench 4 / 8 to finish on 9 hosts (step = 3): should take 10 seconds
INFO:health_protocol:CPU: Waiting bench 5 / 8 to finish on 12 hosts (step = 3): should take 10 seconds
INFO:health_protocol:CPU: Waiting bench 6 / 8 to finish on 15 hosts (step = 3): should take 10 seconds
INFO:health_protocol:CPU: Waiting bench 7 / 8 to finish on 18 hosts (step = 3): should take 10 seconds
INFO:health_protocol:CPU: Waiting bench 8 / 8 to finish on 21 hosts (step = 3): should take 10 seconds
INFO:health_protocol:End of job cpu_load
INFO:health_protocol:Asking 21 hosts to disconnect
INFO:health_protocol:Still 0 hosts connected
INFO:health_protocol:All hosts disconnected