Add support for json style output fot all labels

[ShirleyFei]

Currently, atop data can only be viewed when logging into a machine.
But sometimes we need to aggregate atop data of multiple machines
belonging to the same cluster, such as aggregation of the same
application processes, and then draw and show historical graphs
for users to query and use.

Considering json is widely used in data processing, this patch will
add json style output as a secondary output path. Three types of
output are supported:

1. atop -O stdio
2. atop -O only
3. atop -O unixsock -w /path/to/file 10
   For 3, make unixsock in a non-blocking state to guarantee it will not
   block main engine forever. Another point is atop will try to reconnect
   to the server and continue to work even if the unix remote server
   relaunches.

Usage examples:
./atop
./atop -P ALL
./atop -O only // overwrite parseout, show json to stdio only
./atop -O stdio -P ALL // both parseout and json stdio
./atop -O stdio -w atop.log // print to stdio, as well as file
./atop -O unixsock // overwrite parseout, show json to unixsock
./atop -O unixsock -P ALL // both parseout and json unixsock
./atop -O unixsock -w atop.log // write json to unixsock and file

The detail json style output format is as follows:
{"ip": "a.b.c.d", "timestamp": 1565256314, ...,
"CPU": {"hertz": 100, "cpu_nums": 40, ...},
"cpu": [{"hertz": 100, "cpu_id": 3, ...}, ...,
{"hertz": 100, "cpu_id": 39, ...}],
"PRC": [{"pid": 1, "p_name": "(systemd)", ...}, ...,
{"pid": 73, "p_name": "(migration/12)", ...}],
...
}

Signed-off-by: Fei Li lifei.shirley@bytedance.com
Signed-off-by: zhenwei pi pizhenwei@bytedance.com

[Atoptool]

This pull request has already been implemented by pull request #214.