HDDS-6641. datanode usageinfo CLI should provide JSON output option

[sodonnel]

What changes were proposed in this pull request?

Add the option for the command ozone admin datanode usageinfo to output as JSON/

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-6641

How was this patch tested?

New unit tests. Also verified the JSON out using a docker-compose cluster:

bash-4.2$ ozone admin datanode usageinfo -m --json
[ {
  "datanodeDetails" : {
    "level" : 0,
    "cost" : 0,
    "uuid" : "cf92907e-ed4d-49e5-9e4e-0283f8815e80",
    "uuidString" : "cf92907e-ed4d-49e5-9e4e-0283f8815e80",
    "ipAddress" : "172.23.0.7",
    "hostName" : "ozone_datanode_1.ozone_default",
    "ports" : [ {
      "name" : "REPLICATION",
      "value" : 9886
    }, {
      "name" : "RATIS",
      "value" : 9858
    }, {
      "name" : "RATIS_ADMIN",
      "value" : 9857
    }, {
      "name" : "RATIS_SERVER",
      "value" : 9856
    }, {
      "name" : "STANDALONE",
      "value" : 9859
    } ],
    "setupTime" : 0,
    "persistedOpState" : "IN_SERVICE",
    "persistedOpStateExpiryEpochSec" : 0,
    "initialVersion" : 0,
    "currentVersion" : 1,
    "signature" : 20570720,
    "networkName" : "cf92907e-ed4d-49e5-9e4e-0283f8815e80",
    "networkLocation" : "/default-rack",
    "networkFullPath" : "/default-rack/cf92907e-ed4d-49e5-9e4e-0283f8815e80",
    "numOfLeaves" : 1
  },
  "capacity" : 62725623808,
  "remaining" : 41445900288,
  "totalUsed" : 21279723520,
  "ozoneUsed" : 8192,
  "totalUsedPercent" : 33.93,
  "ozoneUsedPercent" : 0.00,
  "remainingPercent" : 66.07
}, {
 ...

[adoroszlai]

Thanks @sodonnel for the improvement. LGTM, with one minor suggestion for the test.

[adoroszlai]

Thanks @sodonnel for updating the patch.