Add field modificationTime for Volume and Bucket

hadoop@1987b5de4203:~$ ./bin/ozone oz -infoVolume /dummyvol
2018-09-10 17:16:12 WARN NativeCodeLoader:60 - Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
{
"owner" : {
"name" : "bilbo"
},
"quota" : {
"unit" : "TB",
"size" : 1048576
},
"volumeName" : "dummyvol",
"createdOn" : "Mon, 10 Sep 2018 17:11:32 GMT",
"createdBy" : "bilbo"
}

hadoop@1987b5de4203:~$ ./bin/ozone oz -infoBucket /dummyvol/mybuck
2018-09-10 17:15:25 WARN NativeCodeLoader:60 - Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
{
"volumeName" : "dummyvol",
"bucketName" : "mybuck",
"createdOn" : "Mon, 10 Sep 2018 17:12:09 GMT",
"acls" : [ {
"type" : "USER",
"name" : "hadoop",
"rights" : "READ_WRITE"
}, {
"type" : "GROUP",
"name" : "users",
"rights" : "READ_WRITE"
}, {
"type" : "USER",
"name" : "spark",
"rights" : "READ_WRITE"
} ],
"versioning" : "DISABLED",
"storageType" : "DISK"
}

hadoop@1987b5de4203:~$ ./bin/ozone oz -infoKey /dummyvol/mybuck/myk1
2018-09-10 17:19:43 WARN NativeCodeLoader:60 - Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
{
"version" : 0,
"md5hash" : null,
"createdOn" : "Mon, 10 Sep 2018 17:19:04 GMT",
"modifiedOn" : "Mon, 10 Sep 2018 17:19:04 GMT",
"size" : 0,
"keyName" : "myk1",
"keyLocations" : [ ]
}